Rust (錆) is the name of the player-controlled character during the Rust chapter, which takes place after Sabitsuki collects 24 effects and goes into flow while already in flow. It is unknown whether Rust is an alternate form of Sabitsuki or a separate entity entirely.
Rust's appearance is that of a darker Sabitsuki; her skin is more pale, and more details are shown. Unlike Sabitsuki, the shadows in her skin, hair, and clothes are clearly visible, as are the wrinkles in her skirt. Also, unlike Sabitsuki who simply has her current effect disabled, Rust, who is unable to collect or use effects, takes physical damage when coming into contact with the Red Demons, and taking too much damage will cause her to die and return to her room.
- Despite not being able to use effects, Rust has access to the areas that Sabitsuki could not reach in the past; the three areas that were previously blocked by static barriers are open to her (see empty boxes).
- If looked closely, Rust, whom is weakened to one more red demon before death, is actually a red demon underneath her skin, or is turning into one. You can notice the horns and teeth.
- Rust in Japanese is read as "sabi".