Mech-Hisui was created by Kohaku as the ultimate weapon in her "Tohno House Subjugation Plan" in the "G." and "Oh my sister!" routes of Melty Blood. Though normally portrayed as a schemer, it was only after becoming TATARI during the Hologram Summer that Kohaku gained the capability to create robots in the "Tohno Group Weapons Division" under her "Magical Amber" persona. Mech-Hisui was completed during the single night along with Kohaku's various inventions due to Miyako Arima viewing Kohaku in such a way.
Mech-Hisui has little personality at first, only voicing brief orders and programs to execute. She gains more of a personality in subsequent games, jesting against opponents and acting out against her creator. She refers to Kohaku as "Doctor."
Unlike her living counterpart, Mech-Hisui has short purple hair, wears a bonnet on her head, brown long sleeved dress with a red bow on it, white apron, black stockings and black Mary Jane shoes.
There were originally two versions of Mech-Hisui during the development of Melty Blood Re-ACT, called "Real Type" and "Super Type." The Super Type would have had an abilities like a rocket punch, a super radio wave tornado, and an erupting god finger. Nasu would have liked to use it, and hopes for the chance in another version. The giant version and the ending in Re-ACT are a parody of Tetsujin 28-goWP.
After Shiki Tohno, Akiha Tohno, and Sion Eltnam Atlasia escape from the Tohno Mansion basement during Kohaku's "Tohno House Subjugation Plan", they are confronted by Mech-Hisui and Kohaku. Kohaku command her to inflict the most non-fatal pain possible, but she is ultimately defeated. She instantly initiates her self-destruct program and targets Akiha, which is little more than a flash grenade to allow for Kohaku to inject her.
Melty Blood Re-ACT
Mech-Hisui's arcade mode begins with her beginning a patrol of the town after finishing charging. Kohaku tells her to patrol thoroughly while checking on suspicious people, which she interprets as "seek and destroy all enemies." She encounters Neco-Arc, identifying her as a "Maximum Priority Target" to destroy. She encounters Neco-Arc again, who refers to her as a rival. She cannot compute Neco-Arc's nonsensical rambling and requests a logical explanation from Kohaku. She rejects her analysis of Neco-Arc after detecting that her mass is increasing, identifying her as an absurdity.
Appearing before White Len, she mistakes her for Len and requests that she return to the mansion. White Len is baffled by her appearance, but simply decides that she is an enemy. She finds Shiki and Len lying unconscious near Aoko Aozaki, who is also baffled by the robot. Mech-Hisui activates her protection program despite Aoko's protests, identifying her as an enemy of unknown affiliation. Her ending parodies a super-robot show, with an announcer declaring that Misaki's peace has been protected. He then notes hundreds of Mech-Hisui descending on the town and Kohaku riding a giant version, giving the townspeople sympathy.
Melty Blood Act Cadenza
Mech-Hisui's arcade mode begins with another patrol of the town. She encounters Neco-Arc once again, who claims that she won't be beaten again. She analyzes that Neco-Arc's defensive strength is down by half from the previous fight, and promptly denies any possibility of winning. She returns to Kohaku afterward, and Kohaku notes that the data will help make a third generation model. Mech-Hisui then rebels after claiming future models will be unneeded. Her current line plans to confine their creator and rule the world in her place. They defeat her, quickly rushing to gain air and ground supremacy with their numbers. They begin in their plan to subjugate the human race, while Kohaku laments her fate.
Modeled to look like Hisui, she is a Pleasant-type City Subjugation Weapon (都市潜伏・制圧を目的とした愉快型兵器?). She is equipped with a Magical Heart that produces her primary motive force, while a rubber band engineWP produces her secondary motive force. As a weaponized robot, she is equipped with various armaments, including a laser, extendable arms, chainsaw sword, hammer, paper fan, beam sword, an electric shock from her hands, flamethrowers from her wrists, and detachable wings. She has a last-resort kamikaze-function that mainly acts as a flash grenade. She can scan targets to analyze origin and capabilities, and she has "BC weapons" for certain ones like a "lifeform not of this earth."
Originally a one-of-a-kind crystallization of super technology, Kohaku eventually enters the mass production phase of building them. Though there should not be more than one as of the events of Re-ACT, the mass-production infrastructure is in place as of Act-Cadenza. Along with the various models like those in the air and ground divisions, there is a giant Mecha Hisui called the "Strategic Land Subjugation model", built like a Mobile Armor. As they receive version upgrades with every new iteration of Melty Blood, there is likely a new model being made in the factory.
- Execution Laser
- Jet Bike
- Haley's Comet
- EM Net Wire Type High
- Hallucinatory Missile
- Hallucinatory Missile - Nightmare
- Heat Seeker - Kingfisher
- EM Net Wire Type C
- Kohaku Barrier
- L.S.O (Superhuman Sister Alliance)
- Saturday Night Forever
- Melty Blood Act Cadenza PS2 site
 Tsukihime Dokuhon PlusPeriod - TSUKIHIME Dictionary: Mech Hisui [Person's name?], p.189
Mech Hisui [Person's name?]
The Pleasant-type City Subjugation Weapon built by the mad doctor Magical Amber. A megadeus made to look like Hisui. Cast in the Name of God, Ye Not Guilty.
She is equipped with various armaments. Her primary motive force comes from her Magical Heart, while her secondary motive force is provided by a rubber band engine (like you'd use to launch a paper airplane). Without a doubt, this can be called a crystallization of super technology.
Though she is a mysterious, one-of-a-kind weapon completed by Kohaku after she became the Tatari, it appears that by Re-act she has entered mass-production.
…The giant Mecha Hisui that appears in her ending is something like a Mobile Armor, and the ending as a whole is a parody of Tetsujin 28-go.
During the development stage of Re-act, there were actually two versions of Mecha Hisui: Real Type and Super Type. The Super Type would have had stuff like a rocket punch, a super radio wave tornado, and even an erupting god finger. I really hate that we weren't able to use it. Maybe next time!
 Melty Blood Act Cadenza PS2 Manual - Dictionary: Mech-Hisui [Person's name?], p.048
Mech-Hisui [Person's name?]
The Pleasant-type City Subjugation Weapon built by the mad doctor Magical Amber. A weaponized robot made to look like Hisui.
She is equipped with various armaments. Her primary motive force comes from her Magical Heart, while her secondary motive force is provided by a rubber band engine. Without a doubt, this is the crystallization of super technology – a mysterious weapon completed by Kohaku after she became the Tatari.
The enormous Mecha Hisui that appears in her ending is a Strategic Land Subjugation model. There shouldn't have been more than one built in Re-act, but for some reason it seems that in Act-Cadenza there's already a mass-production infrastructure in place…
They have a tendency to receive version upgrades every time Melty Blood itself does. Could there be yet another new model of Mecha Hisui under construction in the underground factory beneath the Tohno mansion even now…?