Hanako is Senpai's younger sister. She loves her big brother more than anything in the world, and depends on him for almost everything. She is very possessive of him, and becomes upset when he won't spend time with her.

After eight weeks away from her brother, Hanako decides that she just can't bear to be enrolled in a different school than her beloved sibling, and transfers into his school so that she can be with him all day long.

Hanako is deathly afraid that if her brother gets a girlfriend, he'll forget all about her and refuse to spend time with her. She has made it her mission to stop him from getting a girlfriend at all costs so that nobody else can have her big brother's attention. Senpai would never want to do anything that would make his little sister cry...this would spell doom for anyone who has fallen in love with Senpai.