Kokari is a young boy with a rabbit fur on his head (it’s the only mammal he’s managed to catch) and lives in Agata Forest with his dog Ume and his father Karude. Fishing is his passion and Kokari hopes to one day become a great fisherman however when faced with the possibility of failure he refuses to try or starts crying.
Ume and Kokari had been exploring the Tsuta Ruins when a loud roar caused Kokari too flee and accidentally leave Ume trapped in the ruins where he was devoured by the Spider Queen. After being rescued it is reveled that Ume willing stayed behind to teach Kokari a lesson in responsibility after he had been reluctant to fix a broken bridge out of fear of failing. Ume was later devoured by the monstrous fish Whopper and despite loosing all his line Kokari continued to try to save Ume. He succeeded and then started to travel the land with Ume as both can be found in Kamui.
In Ōkamiden Kokari has returned to Agata Forest with no reason given for his return or mention of his time in Kamui. He captures the mermaid Nanami and is talk into sacrificing her to a giant catfish called Bullhead by the locals who want the giant fish to stop terrorizing the area. Kokari later comes to regret his actions and helps Chibiterasu save her. Nanami is grateful to Chibiterasu but continues to despise Kokari and claims she can no longer stand any human. Eventually Nanami comes to forgive Kokari and the two can later be seen hanging out.