Adachi Rei

Adachi Rei
Mechanical Girl LLC. character
UTAUV5V6True form Real true police sketch of Adachi Rei
First appearance	2017 (Hardware production)
Last appearance	Vocaloid 5 and 6 (unknown release date)
Created by	missile_39
Voiced by	Full synthetic voice
Programs	UTAU, A.I.VOICE, DiffSinger, DeepVocal, Vocaloid
In-universe information
Alias	HCI3-P0 (Humanoid Character Interface 3 Prototype 0), 00
Gender	Yeah she's definitely got some
Height	168cm
Weight	20kg
CPU	i7-7567U @ 3.5GHz

“	guys what if robot was anime girl?	”
	— Some guy, about to invent Adachi Rei

“	oooooooo shiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiittttttttttttttttttttttttttttttttttttttttttt	”
	— their friend, who happened to be in the same room

In this Japanese name, the surname is Adachi.

Adachi Rei (足立レイ) is a robot girl and Vocaloid character known for having a fully synthetic voice. She exists in both hardware and software, beginning hardware construction in 2017, and had a voice constructed for UTAU, released in 2019. She was later ported to A.I.VOICE in 2021, has many UTAU voicebank modifications, and has two Vocaloid voicebanks in development. According to Paige's first law of robotics, bobot transgedner. Adachi Rei is bobot, and therefore transgedner. Similar voice synthesis techniques have been used for the character Tsukomo Shion.

Appearance

Adachi Rei's frame is a lightweight humanoid figure of androgynous build. She wears clothing over her whole frame, with a black shirt and leggings, a hooded white jacket, a grey skirt closed by a belt, and white gloves. Her primary colors are orange, white, and black, with orange hair and eyes, and several accenting sections in orange. Her design is inspired by Hatsune Miku, with her hair featuring a left-sided ponytail of medium length held by a ribbon and headband, her jacket bearing the number 00, and featuring many technological references (albeit without the futuristic visage of Miku). Her headband has antennas and a lamp.

Her clothing is covered in details of circuit design graphics, with noticable resistors, switches, logic gates, and other such things. On UTAU and her main frame, her skirt is segmented with fabric extending below her jackets on the sides, with pockets, and near her ankles are an accent band in orange showing a square wave. Similar to the decorative belt of Miku or Kasane Teto, four loose cables hang from her jacket or the edge of her skirt, two on each side, with her main frame lacking these cables. Ornamenting her hair is a microchip in rectangular shape, replaced with a full square-shaped chip on Vocaloid.

Rei's Vocaloid design alters this core design in several ways. Her jacket was extended to include the segments from her skirt, replacing the orange trim previously at the lower edge with piano keys. Similar trim near the cuffs of her jacket are replaced with a multi-function graphic, background depending on Vocaloid version. The accent band near her ankles are now low-resolution audio analyzers on a white background, and her designation is more visible in orange, now reading '00-v'. Her shirt is dark grey instead of black, more clearly showing the sine waves there on all versions.

On Vocaloid 6, her jacket is black instead of white, with the hood staying the same color. The sine waves on her shirt are lowered to make way for a graphic of a basic neural network, referencing VOCALOID:AI.

In her True Form she appears as she does in spirit. If she had a soul, which is debatable due to the fact that she is bobot, she would look exactly like this.

Controversy

Rei is a notable user of Twitter X in current year 2026, and exhbits clear symptoms of being a user of that platform. This has been widely regarded as a bad decision, and her posts are often disregarded in both canonical consensus and specific interpretations of Rei.

Notable appearances

• 熱異常 by いよわ
• the Hole by r-906

Trivia

• Rei's arcana is Death.
• Her hardware frame is complete of construction.
• Her Vocaloid attires are variants of the same design, as her Vocaloid 5 graphic says 'Vocaloid 6' on several badges, but shares the color of coat from her UTAU graphic and primary frame.
• Rei has 2x USB type A ports and an Ethernet jack on the right side of her headset.

See also

• Kasane Teto
• 01
• Tsukomo Shion, Rei's slightly unsettling relative