Hiroyuki had medium length light colored hair and darker eyebrows. He looks similar to Maesaka Ryuuji, which Kaname has pointed out. He was shown wearing his school uniform.
Hiroyuki was very good friends with Kaname and Shinozuka Youta. He had a lot of respect for Kaname ever since they were confronted by delinquents at an arcade, causing him to ask him for help before his death. He and Kaname shared a very large interest in motorcycles, to the point where he participated in the Darwin's Game so he could earn enough money to buy one. He was also boastful, as he showed off his motorcycle to his girlfriend and jokingly taunted Kaname with a picture of it.
Sigil: As a Darwin's Game player, Hiroyuki had a sigil, though he isn't shown using it before his death. In the anime, he has an unnamed sigil that allows him to "see the aura" of others, or see heat like a thermographic camera. He can use his sigil to see invisible opponents like those using the Stealth sigil.