He is very organised and smart. While Chiaki and Makoto like to do fun things. He prefers to spend his free time in the library. But he enjoys hanging out with Chiaki Mamiya and Makoto Konno, especially playing baseball or catch.
He borrowed Makoto's bike, which had a broken brake, to take his girlfriend, Kaho Fujitani, to his father's clinic to check on her ankle. Makoto ran after him to try and stop him from dying. But when she thought he hadn't gone through the hill, Kosuke passed her and greeted her while on the bike with the broken brake. Makoto tried to stop him but she fell miserably and started crying. Then Chiaki used his last leap to stop time. Because he didn't want to see Makoto suffer.