The unfortunate new homeroom teacher at this unusual school, who really has no idea what she's gotten herself into.
An extremely earnest young woman, she can end up letting people walk all over her in her efforts to accommodate them. She's perhaps best described as 'unassuming'—or, more to the point, 'cowardly.' She wouldn't look out of place as a nameless NPC in some generic role-playing game. She doesn't have much luck at work; she's the type to end up causing a huge calamity, and then get caught out straight away by her superior.
According to Arisaka herself, she was equally unlucky as a kid—she's always drawn the short straw. Sometimes it can genuinely seem like she's cursed.
Other than that, though, her life is pretty ordinary. Mundane, even. That can seem like a breath of fresh air somewhere like Mihama Academy. Like everyone else, she appears simply to have drifted into the school.