Yōsuke-kun has the appearance of a teenage boy with pale skin, shadows under his eyes, messy turquoise hair and eyes. He wears a middle school uniform, or gakuran, consisting of a long-sleeved black shirt with several gold buttons, black pants and white shoes. He is noted by Sunakake-Babaa to be rather handsome.
He has a creepy demeanor and is rather obsessive, having sent gifts and flowers to Hanako-san and kept watching her. He is oblivious to his actions, believing that their love is genuine, and will get rid of anyone he thinks is in his way with Hanako-san.
When Mana calls Neko-Musume for help because of strange occurrences happening to her, Neko-Musume speculates that it could be one the yōkai haunting her school. Which Mana lists her school's seven mysteries, among them is Yōsuke-kun who can found on the second floor's boy's bathroom. Neko-Musume mentions that she does not know Yōsuke-kun, but is a friend of Hanako-san, and decides to ask her about this. Later at night, when they and the others have cornered Nezumi-Otoko in his stall, Yōsuke-kun appears behind him, asking why he is talking about Hanko-san, causing him to reveal his presence to the others. He steps out of the stall and claims he does not have business with Mana and instead drags Nezumi-Otoko away. They later find Nezumi-Otoko and the other Seven School Mysteries, who are dangling from the ceiling in the gymnasium. He shows himself and claims that Nezumi-Otoko was after Hanako-san, which he confesses his love with Mana, but she denies it. After his rope breaks and as he tries to escape, Yōsuke-kun chases after him demanding to know where Hanako-san is.
After a while, Neko-Musume stops them, and asks if he and Hanako-san are really a couple, because she never mentioned him to her. He claims that they are and that she is shy, to which Ittan-Momen asks what he does. He states that he sends her gifts and flowers and is constantly watching her, to which everyone points out that he is merely a stalker. Yōsuke-kun refuses to believe their reasons of why she is not in love with him, telling them of how they fell in love, in that one night he ran out of toilet paper and Hanako-san gave him some to use. Nezumi-Otoko sympathizes with him, understanding his love and claims that they are kindred spirits, joining together. Nezumi-Otoko makes him believe that they tried to mislead Hanako-san from him, but in reality, Hanako-san ran away because she was frightened of him. He refuses to believe Neko-Musume's response and attempts to punch her, but is stopped easily and beaten by her. She explains to Yōsuke-kun that he is too enwrapped by his selfish desires and then finishes him off, causing an explosion. His soul then flies to someplace else.
Levitation: Yōsuke-kun is able to float just above the ground, as demonstrated when he was dragging Nezumi-Otoko to the gymnasium.
There are numerous variants of the Hanako-san legend in the various prefectures of Japan, and Yōsuke comes from the variant from Yokohama in the Kanagawa Prefecture. According to this variant, there is a Yōsuke of the male toilet in addition to Hanako of the female toilet, who will kill you if you do not escape after calling him within three seconds. Moreover, it was also said if someone calls "Hanako-san" three times around the male toilet, a bloodied hand will appear from the toilet.