Nijiiro Days (MIZUNO Minami) Manga
There on the other and Na-chan, who's bullying, and on the other side Mattsun who's popular. there's also Megumi-chan who's a sadic and Tsuyobon who's an anime otaku. And then those 4 are interweaving with both of their year and that's the beginning of silly and thrilling love stories.
But at christmas eve, the heartbroken Nacchan met someone who has the uniform of Santa ?!