He is the eldest son of the other Minami family. It seems that he is working from the way he dresses. His name hasn't been revealed yet, though if it follows the "spring, summer, autumn, winter" naming pattern it would contain the kanji for "spring". Though calm and composed in his demeanor, it seems as though he is in a state of denial concerning the adverse effects the brothers' lifestyle is having on their younger sister.
(Source: Wikipedia)