Io has dark hair and an ahoge. He has black eyes, and wears glasses.
He is dense and stoic, yet kind at heart. He is oblivious to Tsumiki 's crush on him, but she is the closest girl to him regardless. He is responsible and independent. Like Tsumiki, he is a good cook, and a genius. He is usually seen spinning a pen with his hand, fast enough to catch Mayoi's surprise at his hand's speed. At times, he unknowingly acts like a casanova. He is popular with cats and girls.
In the manga, he is able to catch a fish with chopsticks, while in the anime, he is able to kill a mosquito with a toothpick. It is unknown if he has romatic feelings for Tsumiki.