I'm Rikuto Miyanaga. A second-year high school student whose age equals the number of years I've been single. This spring, I, who have zero immunity to girls, got a younger step-sister——. And not just one... but five!? The eldest, Chinatsu, is a huge man-hater. The kind-hearted second daughter, Mio, and the gal third daughter, Karin, are twins. The fourth daughter, Fuuka, is a young lady with a secret, and the youngest, Sorane, is a spoiled baby! Our sudden life together is a chaotic life full of trouble! I'm starting my "Big Brother Life" with five step-sisters, each with their own unique color!