- Hiyori Asahina: Hibiya had a crush on her, but she would not notice him even if he was popular with other classmates. He often performs strange activities around Hiyori, such as keeping a cherished photo of her in his wallet and creating a miniature Hiyori-doll, complete with her voice recordings that allows it to speak. At one point of the story, he is shown running any errands that she requests despite his discomfort of the city. He hopes to win her affections by presenting her with a dinosaur keychain, which she detests. He feels bad if he disappoints her, and tries hard to win her approval. She visits the city to take summer courses with Hibiya at her relatives' house, but during an accident on August 15th the two come into contact with the Heat Haze and get involved in a groundhog-day loop in which one of them will die within each loop. Eventually Hiyori dies whilst Hibiya is granted a snake which subsequently allows him to leave the Haze.
- Konoha: Konoha is like a brother to Hibiya and Hiyori. He was always with them before the time loop; Konoha tried to save him and Hiyori when they were stuck in the time loop. At first Hibiya hated Konoha for making Hiyori ignore him. He enjoys Hibiya's cooking. Konoha made Hibiya a promise to bring back Hiyori, which is fulfilled at the end of the anime.
- Azami: Hibiya and Hiyori were stuck in a groundhog-day loop on August 15th, Azami's birthday. Azami is described as the Kagerou Daze who caused the loop.
- Momo Kisaragi: Momo and Hibiya tend to fight about the smallest things, their quarrels are endless. But even though that, Momo is probably one of the people he's most grateful for, as she helped him standing on his own feet again, telling him not to give up yet. They tend to stick together, though it's usually Momo who actually tries to get closer. Hibiya, funny enough, doesn't seem to mind this.
- Ayano Tateyama: Hibiya had a conversation with her in the time-loop before he woke up in the hospital. In the manga, he appeared to meet with Ayano outside of the Heat Haze, where she claimed that she could tell Hibiya "the truth".