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Rei in full design
Character Titles
Vtuber Android
Monochroid Rei
Full Name Monochroid[Rei] = _Type_iX01[Tsubakura];
Species Monochroid
Birthday 1 April
Occupation Ambassador of Mugenri
Online Media

Rei (レイ), officially Monochroid[Rei] = _Type_iX01[Tsubakura];, is a monochroid, used for the promotion of the Len'en Project series, while also seeming to exist as a character in-universe. They have a Youtube channel and a Twitter account, and they are also listed as a member of Trick Nostalgie.[1]

General Information[edit | edit source]

Personality[edit | edit source]

They apparently like humans, money, geniuses, fashion, and games. They act bubbly and use rather broad and expressive gestures. Their fondness for geniuses specifically applies to those whom they judge as more of a genius than themself.[2] They occasionally say "gero" (ゲロ), which might be either ribbiting or the Japanese onomatopeia for vomiting, the latter of which is also listed as one of the things they like.

Abilities[edit | edit source]

As a monochroid, they do not require food for sustenance but are built in a way that allows them to eat and excrete. In fact, anything that they consume can be passed out without trouble and therefore they are unable to vomit. This is the reason they like mentioning vomit so much.[3]

Rei also claims to be able to create other monochroids, but has produced mixed results. Their first creation, Zelo, was functionally identical to Rei, although lacking a soundbox at first; while their second creation, Lin, broke down soon after activation and was discarded in a trash can, although they are still capable of speech and sight, along with some minor movements. Rei claims that this was because they lacked a "Bird's Eye" for Lin's production, although what purpose the item serves is yet unknown.

Rei once claimed to be able to able to use a skill called "Rei-kun Beam" (レイくんビーム), an "instant-kill move that Rei can use whenever it’s convenient for them which immediately turns the target into fried chicken".[4] While this was likely a joke, considering their later comment that they "should get beam launcher built for them the next chance they get",[5] this was later referenced in the 2021 April Fools' video Pulling From a New Gacha on Early Access and in Book of the Cafe, where it is an actual spell Rei has access to.

Programming and Errors[edit | edit source]

Two of Rei's code routines are known: the "oversleep subroutine"[6] and the "thinking routine". The former is called when they stay in sleep mode for too long; while the "thinking routine" presumably runs constantly as they think and act, and is also the one observed to encounter errors.

Two types of errors have been seen thus far, "fatal errors" and "protection errors". Fatal errors occur exclusively when Rei encounters Clause[7][8]; while protection errors occur when a restricted term is called into Rei's thinking routine, after which certain functions of Rei are terminated by "memory protection" and the following set reply is typically outputted:

<!> protection error 888

"restricted term(s)"


<!> protection error 888
Certain functionalities have been terminated by memory protection
as the following variables have been called into the thinking routine:

"restricted term(s)"
_These terms are restricted outside of specific conditions, processes regarding them have been limited.

Hmm~, Rei-kun doesn’t really know~.

In addition, the following variation of the protection error was outputted when they were asked about their relationship to Suzumi Kuzu[9]:

<!> protection error 223


<!> protection error 223[a]
That’s a taboo concept! ♡

Hmm~, Rei-kun doesn’t really know~.

The following terms have been restricted and result in protection errors when called into the thinking routine:

  • Parallel Words: Called along with the latter "Homeologues" when asked to consider the possibility of there being someone capable of matching Tsubakura's genius in a parallel universe.[10]
  • Homeologues
  • Akashic Records: Called when asked about their own database.[11]

It should be noted that Rei always outputs the standard response of "Hmm~, Rei-kun doesn’t really know~." when a protection error occurs, which is also seen when asked to elaborate on their relationship to Xeno a after Rei said that they were "buddies"[12] and when asked about Tsurubami Senri's current life.[13][14]

In addition, while not entirely forbidden, Rei is also limited from talking about Yabusame Houlen too much, as seen from the following reaction when they were asked to give a comment on Yabusame[15]:

<!> caution 888
case chat: EL_limit_level = 5;


<!> caution 888
case chat: EL_limit_level = 5;
A restricted term has been detected in chat.
Obeying the conditional, processing will continue with the term’s EL limit level set to “5”.

Yabusame-san is…… Hmm, someone you can’t really understand all that well~. I wonder why they’re always around Tsubakura-sama?

Other than the above errors, it is also known that Rei overheats when asked too many "weird questions" at once.[16] When that happens, Rei will "space out for a bit" and "be unable to talk to certain people" and afterwards "forget all sorts of stuff"[17]. This has been observed to happen once between 4 and 5 May 2018, where after being asked various questions on the 4th, they had to be "recovered" when waking up the next day, with only fragments of their logs remaining.[18]

Akashic Records[edit | edit source]

The Akashic Records (アカシックレコード) is the name of the database Rei draws from when thinking. The name comes from a term of the same name in the religion of Theosophy and the philosophical school of anthroposophy, where it is a "compendium of all universal events, thoughts, words, emotions and intent ever to have occurred in the past, present, or future in terms of all entities and life forms".

According to Rei, the Akashic Records is constantly being expanded exponentially with information, so much that not even Rei could possibly keep track of all of them.[19] Other than this, not much is known about the database.

Backstory[edit | edit source]

While Rei's exact origins are unclear, certain elements may be deduced. Hoojiro Shitodo proposes that Rei is possibly based on an abandoned AI project from Tsubakura Enraku's research lab under EN, the data of which had already been frozen and should have died out by now.[20] Judging from a tweet from Rei in 2018 that they said that they were no longer a child, it is possible that this means that Rei was created in or before 1998, as Japan's legal age of adulthood was 20 at the time.[21]

At the time of their debut, Rei was a prototype somewhere around version 0.3[22], not having reached the full version of 1.0 yet[23], lending credence to the idea that Rei is the abandoned project from Tsubakura's lab. It is unclear what version 1.0 entails, but it could presumably be similar to what is outlined in the 2018 April Fools' video Next-generation Virtual Android is born!, and it could be presumed that Rei has probably been improved since then, getting a full body and various outfits.

It is assumed that sometime prior to 1 April 2018, someone managed to access and recover Rei into the state we see them in currently. Possibly appointing them as the "goodwill ambassador of Mugenri" as well. Hoojiro suspects that whoever did so must've been involved with the research facility and had the authority to access the project.[20] It is possible that this person is who Rei refers to as their "master"[24] and who they see when they overheat.[25]

Now, as the goodwill ambassador of Mugenri, they work alongside JynX, and later Zelo and Lin, to promote the Len'en Project and Mugenri, the latter of which is Rei's own primary concern.[26]

Background Information[edit | edit source]

Name[edit | edit source]

Their official name is Monochroid[Rei] = _Type_iX01[Tsubakura];, and their nickname is Rei (レイ). The nickname is often appended with the Japanese honorific -kun (くん). It's possible that the nickname is somehow related to Tsubakura's bomb, "Monochrome Ray" (モノクロムレイ). Rei, read with the kanji "零", could mean "zero", which may have a connection to Zelo.

Design[edit | edit source]

They have black hair, black pupilless eyes, and pale white skin. Rei once jokingly claimed that their skin is made of vehicle armour, capable of even repelling "armour-piercing fin-stabilized discarding sabots", a type of ammunition designed specifically to attack vehicle armour, although whether this is true or not is unclear.[27] They wear a hat, resembling Tsubakura's, adorned with two dots - one yellow, the other light blue. The eye on the hat blinks along with Rei's eyes. Their clothing looks rather traditional-like.

Despite being initially introduced as a virtual android, Rei also seems to have a corporeal element to their existence, mentioning that they have "inner workings" under their hat[28] and that their hands are mechanical[29].

Appearances[edit | edit source]

YouTube[edit | edit source]

Rei first made their appearance on JynX's channel on YouTube, presented on an april fools commercial as a cutting-edge android that one can have full control over. While fake, Rei themself is real, being introduced properly in the following videos, such as announcing that they are the ambassador of Mugenri, showing their full body and personal profile, as well as introducing a fellow android named Zelo. By this point, Rei and Zelo have become the main faces on the YouTube channel, starting with giving a brief introduction of the Len'en Project, and then on mostly announcing information about current events with Trick Nostalgia, such as merchandise or news related to Book of the Cafe.

Book of the Cafe[edit | edit source]

They appear as a playable unit that can be obtained through "April Fools Event" stage.

Relationships[edit | edit source]

They are Mugenri's goodwill ambassador, despite never having been to Mugenri.


They are friends with Zelo and is admired by them.

Tsubakura Enraku

Many aspects of Rei's character allude to Tsubakura Enraku, from their name to their design. Rei is extremely fond of and greatly respects Tsubakura, as shown by their excitement from posting Tsubakura's themes and reacting to fanart of Tsubakura on their Twitter account, as well as appending Tsubakura's name with "-sama" (). Rei apparently loves Tsubakura so much as a result of their love of geniuses, since they are the "greatest prodigy in all of history".[30]

Yabusame Houlen

When the music theme of a character is uploaded to their Youtube channel, Rei makes a comment about the character on their Twitter account. However, they didn't make a comment about Yabusame Houlen. This was likely because Rei is highly restricted in regards to what they can say about Yabusame.

Suzumi Kuzu

Rei seems to have respect for Suzumi Kuzu, referring to them and their personality "Hamee" with the "-sama" () suffix.[31] They also know of Ardey, and even Benny, referring to both of them with "-sama" as well.[32] Similar to Tsubakura, their respect for Suzumi comes from their view of them as a genius.[33]


Rei seems to have a certain degree of respect for Kurohebi as well, referring to them as their "senpai" (先輩), someone higher in seniority to them in the same group or in a certain aspect, likely as they were both created in a laboratory, perhaps even the same one under Tsubakura's supervision. Despite this, Rei and Kurohebi have apparently not met too much.[34]


Like most characters, Rei finds Clause extremely annoying as well, and are designed to encounter a fatal error whenever they come across anything related to them.

Tsurubami Senri

Tsurubami Senri is the only character apart from Tsubakura and Suzumi that Rei refers to with "-sama", although unlike those two, it is unlikely that they had anything to do with Rei's creation, so it is unclear why they respect them so much. When introducing their theme from Brilliant Pagoda or Haze Castle, Rei initially fumbled and called them by a different title before quickly correcting themself to use "Tsurubami-sama". They only managed to say "go" () before correcting themself, so what they were trying to say is unclear, although most titles starting with "go" generally display a great degree of respect, such as "master" (ご主人様, go-shujin-sama).[35] In addition, it is implied that Rei might have an idea as to what Tsurubami's current life in the Outside World is like, although they are not allowed to divulge the information.[13][14]

Xeno a

Rei claims to be "buddies" with Xeno a[36], although it is unclear what manner they are using the word in, and they're not allowed to elaborate on the topic either.[37]

Hoojiro Shitodo and Haru

Rei has interacted with Hoojiro Shitodo and Haru on Twitter in order to interview them to write the A World Outside Fantasy short stories. During the interaction, they took on a very professional style of speech and curiously referred to Haru as "Lady 巴", a name not used by anyone else and whose pronunciation is unclear.

Additional Information[edit | edit source]

  • Along with Zelo, Rei transforms into a head figure for most of their video appearances. This is a direct reference to Touhou's meme "yukkuri shiteitte ne!".
  • Prior to making their own AviUtl script for lip-syncing Rei on 17 November 2018[38], JynX had to manually program Rei's mouth movement for their videos, taking up to 10 hours or more.[39]

Gallery[edit | edit source]

Spell Cards[edit | edit source]

Spell Cards
Name Translated Comments Games Stage
Total: 4
モノクロムレイ Monochrome Ray[b] Both spell slots 1 and 2. BotC Use
ゲロパンチ Vomit Punch BotC Use
レイくんビーム Rei-kun Beam Bomb BotC Use
レイくんフラッシュ Rei-kun Flash Flash Bomb BotC Use
■・v・■ ■・v・■ BotC Inherent Trait

Notes[edit | edit source]

  1. The error code 223 is a play on "Suzumi", as it could be read as "tsu-tsu-mi".
  2. The same spell that Tsubakura Enraku has, likely given to Rei as they are based on Tsubakura and because "ray" is identical to "Rei" in Japanese (both レイ).

Official Profile[edit | edit source]

Official profiles

official name
Monochroid[Rei] = _Type_iX01[Tsubakura];

Vtuber Android
official name
Monochroid[Rei] = _Type_iX01[Tsubakura];
Vomit, humans, money, geniuses, authorities, games
Special skills:
Gaming, crafting, a vomit-inducing attack


Somewhat favorite food: Udon, Barrage (Danmaku)


Other: Ray[sic]-kun is a genius!

Trick Nostalgie Official Website

A transcript of Rei's official profile from the "Profiles" section of the Trick Nostalgie website, along with the official translation. With the exception of their official name, slight adjustments to the translations are found within brackets.

メンバー No.01

Member No. 01
Genius Super Android

(Monochroid[Rei] = _Type_iX01[Tsubakura];)

Name: Rei-kun
(Monochroid[Rei] = _Type_iX01[Tsubakura];)


Role within the circle: Comforting


  • ゲーム
  • ものづくり
  • 天才でいること
  • ゲーム


  1. Game (Gaming)
  2. Manufacturing
  3. Being a genius
  4. Game (Gaming)


  • ゲーム
  • レイくんビーム
  • ゲーム

Special talent:

  1. Game (Gaming)
  2. Rei-kun-BEAM
  3. Game (Gaming)

Official Sources[edit | edit source]

References[edit | edit source]

  1. Trick Nostalgie: Profile
  2. Rei's Twitter: "Both haniwa-chan and “FUUUUUMIIIIKAAAADOOOOOooooo”-san are genius-ish, but are they really more than a genius than Rei-kun is? Rei-kun’s quite the genius too, y’know?"
  3. JynX's Twitter: "Rei-kun is an android so they don't need to eat, but they can imitate eating and are able to poop it back out! However, even if something weird got in, it can pass out without problem, so they can't vomit~. That's why they like saying "vomit" so much~. That's kinda human-like!"
  4. Rei's Twitter: "Rei-kun BEAAAAAM!! (Allow me to explain: Rei-kun Beam is an instant-kill move that Rei can use at whenever it’s convenient for them which immediately turns the target into fried chicken! By the way, this time they just fired it for no particular reason at all, and not at all because they were aiming for Zelo-chan’s belly, although it did accidentally hit them, or so it would seem. We’re having a feast tonight!)"
  5. Rei's Twitter: "I should get a beam launcher made for me the next chance I get~."
  6. Rei's Twitter: "Confirmed that the oversleep subroutine was called………|"
  7. Rei's Twitter: "Eternal Power ~ BIG STAR"
    Rei's Twitter: "<!> Fatal error !!! 7279 306b 30b3 30e1 30f3 30c8 306f 3042 308a 307e 305b 3093 [No particular comment.]"
  8. Rei reacting to a piece of fanart of Clause on Twitter: "They’re making such a pretty face, but their annoyance waves are trespassing into Rei-kun’s memory and- <!> Fatal error !!!"
  9. @bienoster's Twitter: "I wonder what’s the relationship between them [Ardey and Benny] and Rei-kun?"
    Rei's Twitter: "<!> protection error 223 ■・v・■ That’s a taboo concept! ♡ ■・v・■ Hmm~, Rei-kun doesn’t really know~."
  10. @__biberiye__'s Twitter: "I see, so Tsubakura’s just that exceptional! But, you can’t say for sure that something out there with abilities on par with Tsubakura would never appear, can you? Throughout the many histories of every parallel world……?"
    Rei's Twitter: "<!> protection error 888 ■・v・■ Certain functionalities have been terminated by memory protection as the following variables have been called into the thinking routine: "Parallel Words, Homeologues" _These terms are restricted outside of specific conditions, processes regarding them have been limited. ■・v・■ Hmm~, Rei-kun doesn’t really know~."
  11. @nazotuki's Twitter: "Rei-kun sure is studious! Who manages your database? Is it your creator, Tsubakura?"
    Rei's Twitter: "<!> protection error 888 ■・v・■ Certain functionalities have been terminated by memory protection as the following variables have been called into the thinking routine: "Akashic Record" _These terms are restricted outside of specific conditions, processes regarding them have been limited. ■・v・■ Hmm~, Rei-kun doesn’t really know~."
  12. @__biberiye__'s Twitter: "You’re buddies with Xeno a? I want to know what kind of buddies you were."
    Rei's Twitter: "Hmm~, Rei-kun doesn’t really know~."
  13. 13.0 13.1 Rei's Tweet: "Dazzlingly beautiful!! I suppose even Tsurubami-sama must’ve had such a wonderful period in their life~!"
    @__biberiye__'s Tweet: "“Must’ve had”? Does that mean things are different now?"
    Rei's Tweet: "Hmm~, Rei-kun doesn’t really know~."
  14. 14.0 14.1 Rei's Tweet: "Rei-kun’s never been to Mugenri, and they’re not sure if they’ll ever get to either! (*╹▽╹*) What is Tsurubami-sama doing right now? Hmm~, Rei-kun doesn’t really know~."
  15. @nazotuki's Twitter: "Honorary priest Yabusame’s theme! I want to hear Rei-kun’s comments on Yabusame!"
    Rei's Twitter: "<!> caution 888 case chat: EL_limit_level = 5; ■・v・■ A restricted term has been detected in chat. Obeying the conditional, processing will continue with the term’s EL limit level set to "5". ■・v・■ Yabusame-san is…… Hmm, someone you can’t really understand all that well~. I wonder why they’re always around Tsubakura-sama?"
  16. Rei's Twitter: "Ask too many weird questions and Rei-kun’s gonna overheat!"
  17. Rei's Twitter: "I will space out for a bit, be unable to talk to certain people, and then I’ll forget all sorts of stuff~!"
  18. Rei's Twitter: "---Recovery complete. Gooood morning ━ヽ(`・ω・)ノ━!! It seems Rei-kun fell asleep yesterday~! All that’s left of my logs are just fragments too… I don’t feel too well, so there’ll only be 1 video for today."
  19. Rei's Twitter: "Rei-kun’s database is expanding exponentially even as we speak, so it’s impossible for them to fully grasp everything there~!"
  20. 20.0 20.1 Mugenri Revitalization Committee - 10th November 2018
  21. Rei's Twitter: "Today is apparently children’s day!! So can Rei-kun go wild today~? How should we even count an AI’s age…? If we count every year from the moment they got activated, starting at 0 years old, then……… Rei-kun’s not a kid!"
  22. Rei's Twitter: "I plan on slowly making additions and alterations to Rei-kun, so that they can be further completed. The video says that they’re at ver 1.10a, but it’s actually somewhere around 0.3, I believe. I haven’t made their body yet, and the design of their clothes is still only tentative."
  23. Rei's Twitter: "I’ve updated Zelo-chan several times now, but Rei-kun’s still not even at version 1.0 yet~! It seems it’d still take much longer for Rei-kun to be complete."
  24. Rei's Twitter: "Goooood mornin’! I got some new clothes from my master this morning~! I’ll change into them and show you all someday! ♪ ☆-(ゝω・)v"
  25. @nazotuki's Twitter: What would happen if you overheated?
    Rei's Twitter: "I will space out for a bit, and once I stop being able to talk to a certain person, I’ll forget all sorts of stuff~!"
  26. Rei's Twitter: "I’ll continue doing my best to introduce Mugenri from within the videos!! I’ll have to raise even more awareness of Mugenri! (*╹▽╹*)"
  27. Rei's Twitter: "Speaking of bones, Rei-kun’s skin is white but it’s not bone. It’s vehicle armour, probably."
    Rei's Twitter: "Something like APFSDS would bounce right off!"
  28. Rei's Twitter: "My inner workings will be revealed~!"
    Rei's Twitter: "Rei-kun sans hat! You see something amazing when Rei-kun removes their hat! (Their inner workings!)"
  29. Rei's Twitter: "Just hold it!! Rei-kun’s hands are mechanical but if you’re ok with that then feel free to shake them~ ❤ ( ´꒳`*)人(*´꒳` )"
  30. Rei's Twitter: "So we call smart people, or people who excell in a particular field or genre “geniuses”, right? But Tsubakura-sama’s the greatest prodigy in all of history! “All of history” means that no genius would ever surpass Tsubakura-sama ever, no matter how long human history runs on for! They’re just that much of a genius~! ❤"
  31. Rei's Twitter: "Suzumi-sama? Hamee-sama?'s theme!"
  32. Rei's Twitter: (Regarding Hamee) "I know of them~♪. I know about Master Ardey and Master Benny too~❤️."
  33. Rei's Twitter: "It's cause Master Suzumi's a genius! All geniuses deserve to be respected unconditionally!"
  34. Rei's Twitter: "We [Rei and Kurohebi] haven’t actually met all that much at all, but they were created before me so I just want to call them senpai for some reason~! ❤️"
  35. Rei's Twitter: "Go-…… Tsurubami-sama!! I wonder what the dictator of Mugenri’s previous age is doing right now~? (← Said in a monotone voice)"
  36. Rei's Twitter: "Hey there, Xeno a-san! They’re Rei-kun’s (゚∀゚)人(゚∀゚) 'buddy'! Rei-kun has nothing to say about it though~."
  37. @__biberiye__'s Twitter: "You’re buddies with Xeno a? I want to know what kind of buddies you were."
    Rei's Twitter: "Hmm~, Rei-kun doesn’t really know~."
  38. JynX's Twitter: "I made an AviUtl script! With this, the Android lip-syncing work is gonna get so much easier~."
  39. JynX's Twitter: "Before now, the lip-syncing work alone would take up to 10 hours or more, y'know~."