Riken is a straight-faced and stoic second lieutenant in the imperial army. He is chosen to be a human representative in the Ministry of Spirit Affairs and is paired with Susukihotaru. When he overhears that she is afraid of him because of his height, he crouches down and asks her if he is still scary. After this, their relationship greatly improved. He cares for Susukihotaru greatly, and she senses this when she injures his hand while she is possessed by a sword. He describes himself as a man of few words and does not have a problem with Susukihotaru reading his emotions.