Mai Zen'in

Maki's twin, a student in Kyoto: she fights with a gun and her technique creates objects from nothing, at a very high cost. She dies creating for Maki the sword that will set her free.

Twins count as a single person to jujutsu: while Mai lives, Maki cannot reach full strength. In the Zen'in spirit room Mai chooses to die and take with her the share of cursed energy holding her sister back.