Kyodai Seido no aru Yanki Gakuen

A yankee boys' school has a sibling system, just like the sister system at a girls' school. Hondo, a yankee who boasts overwhelming strength, is begged by new student Kurosu one day, "Please be my big brother!" Unknowingly, Hondo finds him cute…!? (originally from cmoa, edited with Google Translate)