Jun is very tall with black hair and black eyes.
When Junichirou is around Tomo, he's playful, slightly aggressive and somewhat clingy towards her. Misuzu remarks that he only really smiles when he's around Tomo. However when he's without Tomo, according to Misuzu, Junichirou comes off as cool and aloof to the rest of the school's population (which makes him popular among girls). He rarely smiles and seems to be easily bored.
He treats Tomo like a guy, he didn't even know she was a girl until they went to the same middle school together. He enjoys spending time with Tomo and (as far as we know) thinks of her as his bestfriend. When they fight they don't hold back and always use their full strength against each other. It is unknown what his true feelings are towards Tomo but he seems oblivious to her feelings of him.
Him and Misuzu do not get along at all. They went out together in their second year of middle school but could only stand three days of each other before they broke up. They've been bitter towards each other ever since.