Say "I Love You".(2008)

Sukitte Ii na yo.

Mei Tachibana has no friends—and she doesn't need them! Ever since her "friends" betrayed her in elementary school, she's sworn off friendship entirely. All it leads to is betrayal and heartbreak, and she's well enough on her own. But everything changes when she accidentally roundhouse kicks the most popular boy in school! However, Yamato Kurosawa isn't angry in the slightest—in fact, he thinks his ordinary life could use an unusual girl like Mei! He won't take no for an answer, and soon Mei and Yamato embark on an unwanted friendship that will change both of them forever.

(Source: Kodansha USA)