He has blonde hair partially covering his face, and is fairly slender. He usually wears a troubled expression.
His pessimism and self-criticism leads to his blaming all misfortune on himself, even when he had no effect on the outcome. However, he is more confident when doing something artistic.
He comes from a family of fishermen, where he did not fit in; he was viewed as being weak and useless, and gets seasick easily. For this reason the other children teased him and the adults pitied him, because he was the eldest son and expected to inherit.
In school, he made a scarf for a girl to give her boyfriend, but the boyfriend found out and the girls blamed the breakdown of their relationship on him. He ruined the sports festival by failing to complete costumes for all clubs, and the teams blamed him for the loss. He discouraged the model-building club by winning an award when he was not part of the club himself.
Because of these experiences he moved to Tokyo to attend university, in the hope of being able to find a place to fit in.
It is implied Ranmaru has a crush on her.
- His catchphrase is "I'm sorry!"