Rust is a playable character after collecting all 25 effects, and then going into flow while in flow, thus examining you computer while in this state. Rust looks a lot like Sabitsuki (and is likely her), but with one difference, her hair and clothes are more detailed and her skin is more pale and her eyes are a very deep red instead of black. She can do many of the things Sabitsuki can, but cannot collect effects.
- If looked closely, Rust, whom is weakened to one more red demon before death, is actually a red demon, underneath her skin (noticing the horns and teeth) or is turning into one. Though, this is likely just blood.
- Rust may have been the diseased part of Sabitsuki or a separate being, though likely the latter.
- Some argue that Rust may be Sabitsuki's alter ego and/or a split personality.