Amagase Just Won't Go Easy On Me.

On the day of her high school entrance exam, Momo was groped by a stranger on the train. Another student heading to the exam, a boy, saved her. Ever since, she's been searching for her savior amongst her new classmates, and has decided that it must be the school playboy, Amagase. His appearance and personality have completely changed, apparently, because Amagase doesn't get serious with anyone. Attempting to appear unfazed, Momo tells (lies to) Amagase: "I will never fall for you." Convenient for a player like Amagase, he forces her to be his next girlfriend. Amagase toys with Momo, his kiss sweet, the physical closeness between boyfriend and girlfriend a first for her... A heart-pounding high school romance with a mysterious boy!!

(Source: MangaPlaza)