1st Year Students
- Fellow member of the Tea Club. Ritsu enjoys being spoiled by Hajime, as well as playing around with him.
- In Phantom Thieves VS Detectives, it is revealed that Hajime tutors Ritsu, despite being in a grade lower than him.
- Fellow member of the same unit, Knights. Tsukasa often scolds Ritsu for his "Unknightly" behavior.
- In Mall Live, Tsukasa mentions that Ritsu is a great dancing coach to him.
- In Test of Courage, Ritsu often enjoyed teasing Yuta.
2nd Year Students
- Adonis has offered to capture Ritsu for Rei, though he declined, as Rei knew that would only anger Ritsu.
- Anzu's fellow second year. Ritsu initially acts standoffish around Anzu. In his first substory, he asks her to either move her phone talk somewhere or die, as he is sleeping in the vicinity. However, having her judge his pastry fairly in Sweets Patisserie improves his opinion on her. He grows fond of her in Duel because she listens to everything he says, and finds her a comfortably silent sleeping pillow with a nice scent. In the same event, he gets a taste of her blood and takes liking to it. Ritsu can often be seen pestering Anzu for blood or lap pillow in following events.
- Dark Night Halloween reveals Ritsu often talks about Anzu to his classmates and refers to her as "hugging pillow" or "emergency ration". They seem to be in comfortable terms where they can tell their worry to each other. Ritsu considers Anzu along his childhood friend Mao the only people who understand him.
- Fellow member of the same unit, Knights. Though Arashi likes to dote over him, Ritsu seems to have little care in regards to him. Arashi also finds the fact that Ritsu being older than him troublesome.
- Ritsu's classmate from 2-B. Ritsu enjoys teasing Koga, calling him "Corgi" and generally being playfully mean to him. In Dark Night Halloween, Ritsu teases Koga plenty by making him eat his sweets, and do things like sing and dance for him, as well as call him "Master" and get walked by him.
- Ritsu's childhood friend who he deeply cares about, and enjoys being spoiled by.
3rd Year Students
- The Captain of the Tea Club. The two tend to bicker over meaningless things, but are otherwise on good terms.
- Fellow member of the same unit, Knights.
- Leader of his unit, Knights. Though Ritsu does acknowledge Leo as Knights's leader and king, he doesn't hesitate to make Leo do slave work for him.
- Ritsu's older brother who he generally act colds towards. His dislike towards Rei is often expressed extremely harshly, such as declining the fact that he has a brother or threatening to kill him.
- In Dark Night Halloween, it was revealed that his brother got him a coffin and regularly uses it, though he dislikes how cramped it is.