Hatsu*haru Vol. 1 (manga)

Playboy Kai definitely knows his way around girls' hearts, but when he has a run-in with tomboy Riko, he may be in for more than he bargained for! Riko definitely doesn't fit Kai's usual type of girl: she's short-tempered, scary, and can (has) easily beat him up. There's no way a rough and tumble girl like Riko is capable of a delicate feeling like love! So imagine his surprise when he finds out about her secret, one-sided crush... But it's none of his concern, right?