He has dark hair and narrow cat-like eyes similar to Hayato's and most of the Kamitani family.
He greatly resembles Hayato, to the point that he is said to resemble his cousin more than his other cousin Taka does. When smiling, he resembles Kotarou in certain ways.
Tsugumi is the son of Shizuka's sister and also the cousin of Hayato and Taka. He was taken care of by the babysitters in the daycare room briefly due to his mother and father being down with a cold in the hospital. He does not take well to Hayato, but calmed down immediately when Ryuuichi proceeded to hold him in his arms.
His presence gained the attention of almost everyone in the daycare room except Taka, who felt jealous about the situation. This forced Taka to resort to childish antics which made Usaida convulse with laughter and for Hayato to chide him for "not setting an example to Tsugumi". Taka, on realising that he is a big brother himself, started behaving well and shared his toy sword with the baby, which eventually shattered when Tsugumi threw it hard against the ceiling. This caused Taka to break down completely and smack Tsugumi on the head, to which Hayato immediately scolded. Taka rebuffed that "he did not do anything wrong" and that "it was his fault", and ran away in tears. Hayato chased after him and comforted Taka, saying that he is proud of Taka for "no longer being a kid" and smiled. Taka decided to apologise and this earned a smile from Tsugumi, but on a change of mood, Tsugumi hit Taka on the head, causing much trouble again for Hayato who called his mother to complain about taking Tsugumi back with her.