Hiroto is a teenager with swept-back spiky black hair and dark gray, nearly black eyes. He is usually only seen wearing his school uniform, but in Rinne Utopia's preview, he is seen wearing a red T-shirt with a white shirt. The collar of his school uniform is often left unfastened. He is 175 cm tall, as stated in the Anime. Hiroto is a rather straight-forward boy who is not shy to express his emotions to the opposite sex, a stark contrast to Shido. He seems to be able to keep his cool under any situation, such as a spacequake. However, this changes when he is interrupted while playing his dating sim. Shido describes Tonomachi as a person that is the best in going with the flow, and good with his words.