She's best known for being the mysterious resident of the school library, where she's apparently been living for a decade. By the time she appears in chapter 75, it's been years since she last fed on blood—specifically not since Hijiri's graduation. The whole time, Hijiri, Higuchi, and Umeko had no idea she was actually older than them, assuming she was in their year.
When she finally gets desperate enough to drink from Olivia, she immediately spits it out. Turns out Olivia comes from a line of vampire hunters, and their blood tastes genuinely terrible to vampires. That's how she figures it out.
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