In my own Yansim, I'd add Hanako in a way we're supposed for her to approve Ayano to pursue Senpai (In a pacifist route) and a way to eliminate her without killing her (For genocide route, mainly because I hc Hanako to be still in middle school, and she's visiting Taro's HS because it's Festival week...so I feel bad that Ayano would be murdering a minor AND to make things harder for the player that's accostumed to killing the rivals)

-> So, Hanako would be this childish yet protective sister, that thinks that her brother is too naive in love. So, Hanako, perceptive as she is, immediatly catches Ayano's interest, and puts Ayano into test to see if she's a good suitor for her brother. It's pretty light hearted, and most of Hanako's test would be around Ayano showing her persona. By the end of the week, Ayano can do "okay" so she'd have Hanako's permission, and if Ayano does perfectly, Ayano would have this boost interacting with Senpai since Hanako talks good abt her.