Boku to Kimi to de Niji ni Naru

Because she loved the word "wisdom", Rui hated the words "waste" and "fuzzy". One day, a guy named Shou appeared on her life. And thank to that encounter, Rui will suddenly change... And that's the beginning of a "rainbow school daze" between that super dry girl and that careless guy.

(Source: Chibi Manga)