Mecha Hisui is a character from Melty Blood, a spinoff of Tsukihime.
Mecha Hisui is a robotic clone of Hisui, created by Kohaku under the influence of the TATARI phenomenon. All mass-produced Mecha Hisui are designed to show complete subordination towards "Doctor" Kohaku.
As a robot, Mecha Hisui is designed with stereotypical anime robot qualities, including eye beams, weapons hidden in her hands, being equipped with a jetpack, and having attacks which reference famous robots from classic anime, such as God Gumdam's Bakunetsu God Finger.
A second Mecha Hisui, who is shown to be in the possession of Neco-arc, was introduced in Melty Blood: Actress Again. This Mecha Hisui has assumed control of it's personality, which results in showing highly rude interactions towards Nekoarc.
She is voiced by Matsuki Miyu.