Mecha Hisui

Kohaku described Mecha Hisui as “Developed in secrecy by the Tohno Weapons Division without Akiha's knowledge, and designed to excel in city infiltration and suppression of the local population. Mecha Hisui is a weapon of pure joy.” Mecha Hisui has a variety of abilities, such as her “Guide and Interfere” function; when used she drags Akiha into a sticky situation and then blows herself up. Mecha Hisui also has the ability “Redoubled Effort” which lets her wrap elastic bands around a target. She is sure to play a major role in controlling Misaki City! But wait, there's more! If you buy one today, you will also get the mass production model for free! Maybe… it all depends on Shiki's fight outcomes, and Kohaku's mood.

MB Official Strategy Guide: Melty Blood Glossary
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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!

Tsukihime Dokuhon Plus Period: Tsukihime Dictionary Revised
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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…?

MB Act Cadenza PS2 Manual: Tsukihime Dictionary