Compared to his brother Mori, Satoshi but is considerably more talkative and outgoing. He is also a devoted member of the Morinozuka clan, going so far as to hit Yasuchika with a stick when he is rude. Satoshi is friends with Yasuchika and cares about him, as demonstrated when he quickly apologizes after making Yasuchika cry. In contrast to Yasuchika's disdain for his older brother, Honey, Satoshi actually adores Mori even though they are so different.
Satoshi and Mori are nearly identical in their appearance, with Mori being slightly taller than Satoshi. Satoshi possesses black hair with grey eyes like Mori's. Satoshi also has a darker complexion, like Mori.
Satoshi is first introduced with Yasuchika in chapter 29, after Honey mentions to Haruhi during the cultural festival that both he and Mori have younger brothers. In a small part of the manga, it's shown that he likes spicy food, after the twins put hot sauce in his tea. Satoshi only appears in the manga a few times, and never in the anime.