Hijiri Kikka

Hobbies: Teasing Senpai (Yuu).
Favorite foods: Ramen and Potato Chips.

"It's been a while! What's up, Toono-senpai! It's your lovely, lovely underclassman, Hijiri Kikka!"

She is a 1st year at Kazami Academy and has no club affiliation. She is Yuu's underclassman, being a year below him.
She won't tell him which class or club she's in for some reason.

She always confuses him by saying "It doesn't matter, does it? Senpai, you totally like me, right?". She easily gets carried away, regardless of the person's age or gender, and gets overly familiar with everyone with absolutely zero distance.

Her hobby is teasing Yuu. It seems she finds his reactions amusing compared to the other guys.

Spoiler

She is the person who saved the protagonist from drowning when he was 8 years old, and she has been in a coma ever since. By the time of the epilogue, she has been in a coma for 10 years.