Beyond that, little is known, due in part to everyone else being terrified of her.
Senpai's cute little sister: a clingy, jealous, and emotionally dependent girl who demands her sibling's attention, so naturally she is a threat for Ayano even if not a typical rival.
Osana serves as a tutorial of sorts for the player and is the easiest rival to defeat. She harbors three desires to be the most popular girl in school, to be the greatest actor to ever live, and to get Senpai. After falling in love with Senpai in a short period of time, she believes there's something supernatural about him.
So, what's a girl to do to keep Senpai for herself?
Why, remove any rivals for Senpai's affection by any means necessary!
Her characterization has been described as pure and innocent, if a little blind to certain implications.
She loves taking care of people, but her klutzy nature seems to cause more problems...