Runa Shirakawa is all sunshine and smiles, while her classmate Ryuto Kashima is more of a gloomy raincloud. No one would've forecast these two getting together, but their relationship has turned into a rainbow of new experiences as they continue to learn from each other and fall deeper in love. As the mismatched pair prepare for the school culture festival, they suddenly find themselves in the same group as Ryuto's first love, Maria - who's also Runa's estranged twin sister! She's already tried to steal Ryuto away from Runa once, and it looks like she's not ready to give up on him just yet!