Nijiiro Days delves into the vibrant lives and romantic escapades of four high school boys: Natsuki, a romantic idealist; Tomoya, a charming ladies' man; Keiichi, a playful sadist with a penchant for whips; and Tsuyoshi, an anime-loving otaku with a cosplaying girlfriend. After a heart-wrenching breakup on Christmas Eve, Natsuki encounters a girl in a Santa Claus outfit who captivates his heart—Anna, a fellow student. His pursuit of her should have been straightforward, but his well-meaning yet intrusive friends can't help but interfere, each navigating their own love trials alongside him.