Description
Mashiro Mutsuki, known as the "Man with the Scar," serves as a major antagonist. He personally attached the irremovable shackles to Jyugo and commands the organization Shiki. A distinctive red scar marks the back of his neck—horizontal with three vertical lines—complemented by his white hair. His face stays largely obscured.

Mashiro displays callousness and disregard for life. He conducts unethical experiments on prisoners like Jyugo and Musashi, aiming to create a "being akin to god." He sacrifices others, including family members, for his research. Elf respects him, while Jyugo calls him sadistic.

His background involves extensive research on "Offenders" (individuals with supernatural abilities) triggered by encountering the escaped Nanba Prison inmate Rokudo. He founded Shiki, an organization claiming to free "togabito" (cursed individuals) from societal persecution and the "Box of Togabito." Shiki's methods contradict this mission: members receive Elf cell implants for surveillance and control, dissent meets violent punishment. Mashiro uses Shiki to further his experiments on targets like Musashi and Noriko Sanzou.

Key experiments include:
* Implanting shackles that transform into weapons, as seen on Jyugo (black shackles becoming blades) and Mashiro himself (advanced shackles forming arm-swords capable of slicing fire).
* Altering memories and creating clones from body parts to resurrect individuals.
* Repetitively cloning his deceased daughter to obtain Rokudo’s child, resulting in Elf’s creation six years later.

Mashiro’s actions fuel vengeful quests. Musashi seeks revenge after wrongful imprisonment and experimentation left him with fire-controlling abilities and facial scars. Similarly, Ikkaku (Inmate 1111), another test subject, bears a lightning-shaped scar and electrocution powers, swearing vengeance.

Shiki’s century-spanning operations target Rokudo for his ability to create more togabito and pursue Jyugo for his unique influence on others’ abilities. The organization collaborates with researchers (Fragment/Team F), but faces betrayal when Fragment steals parts of a crucial "key" containing togabito records.