Nijiiro Days follows the colorful lives and romantic relationships of four high school boys: Natsuki Hashiba, a romantic dreamer; Tomoya Matsunaga, a narcissistic playboy with multiple girlfriends; Keiichi Katakura, a kinky sadist with a whip; and Tsuyoshi Naoe, an otaku with a cosplaying girlfriend. When his fiancée rejects him on Christmas Eve, Natsuki sobs in the middle of the street and is provided tissues by a girl dressed as Santa Claus. He falls in love with this girl, Anna Kobayakawa, who happens to go to the same school as him. Natsuki's pursuit of Anna should have been straightforward and uncomplicated; nevertheless, to to his chagrin, his curious friends frequently intrude in his relationship, as they do in everyone else's.