He's a pretty nice and energetic guy, although he is quite hotheaded. He also is rather sarcastic and has a nasty side to him that showed itself during his first meeting with Seishuu, where when he was talking to Miwa and Hiiro he stated he admired Seishuu and felt he was far away from him until he "accidentally" took away first prize from him and then felt he was on a similar level to him. He also stated he believed that he was just holding back. This sounded rather sarcastic and condescending. He is also rather honest to the point of being rude as shown when he stated Seishuu should return to his old style of doing calligraphy because his new style sucked and was trying too hard to be individualistic. He used Seishuu as a template for his own work so once Seishuu changed his style Kosuke couldn't cope with the change and fell into a slump as well. He is more of an indoors person as shown when he was trying to fish and kept complaining about being outside. However, he begins to change and realize that he needs to find his own style while apologizing to Seishuu for all the rude things he said to him.
He was the boy who won the first place in a calligraphy contest where Seishuu ended up in second place. He later on comes to the Goto islands with Kawafuji. There he tries to bring Seishuu back to Tokyo. He thinks Seishuu's calligraphy changed after he came to the village, but Seishuu told him that the calligraphy that Kosuke likes was the calligraphy his father taught him and on this island he's going to find his own calligraphy. So Kosuke hasn't got an other option but to accept this.
Later on Kawafuij reveals Kosuke isn't writing right now. Not since he saw Seishuu's latest work. Kosuke's been writing with Seishuu's calligraphy on his mind all the time. That's why he got anxious, he lost his point of reference when Seishuu changed his style. Kosuke's calligraphy looks just like Seishuu's old style and Seishuu's old style looked just like his dad's.
- He is scared of bugs.
- He is 18 but people often mistake him for being a middle schooler.
- Kawafuji describes him as quirky and Seishuu says he has a nasty side that shows itself.
- He is more of an indoor person.
- He has stated that he has no friends.
- He doesn't seem to like kids though pretends to in order to look good for the media.
- He has a collection of calligraphy magazines that all feature Seishuu Handa.