Senpai to Boku no Natsuyasumi no Koto

Ayaha is a beautiful, but slightly eccentric bookworm of a girl, a year older than Makoto, so she calls him "boy," even though they both serve on the library committee. As the two begin to interact with each other, Ayaha shows her interest in activities other than reading, and Makoto is constantly surprised by her aggressive teasing. Their young desires gradually escalate with kissing, stripping, and petting....... Now it's summer vacation, a very important time for both of them!

(Source: Otona Bunko, translated)