Nanjiro is often seen rallying against Ryoma. He is also often seen taking advantage of his son and tricking Ryoma to do some things he does not want to do even if it is against Ryoma's will. Despite the unusual parent relationships Nanjiro is Ryoma's tennis mentor - Ryoma has been training under his father since the very beginning (he has been introduced to tennis at the very young age of 2 years old). He has become Ryoma's rival and has trained Ryoma until his match against Yukimura Seiichi in the Nationals. He often says that Ryoma is 'mada mada daze', and that he had a lot further to go. It was revealed in an anime episode that Nanjiro had suddenly retired to train 'his new rival', meaning he had quit to focus on Ryoma's upbringing.
He seems to have a detached way of raising Ryoma, often choosing to watch over him from afar rather than directly interfering with his life. This was demonstrated when he left the amnesiac Ryoma alone, believing that he could overcome his amnesia by himself. He will only step in when it requires Ryoma to train with him or when Ryoma is in danger.
Nanako is Ryoma's cousin who is often seen looking after Ryoma when his mom is not around. Which side of his family she is from is unknown. She has become like an older sister to Ryoma, and has come to treat him like a younger brother. Despite being older than him, she addresses him politely as 'Ryoma-san'.
Ryoma's himalayan cat which he deeply cares about more than anything (beside tennis). He is always playing with him and sleeping together. He and Karupin care about each other. In a fanbook, Ryoma mentioned that he liked cats because of their whimsical nature and the fact that their meowing calmed him down. Karupin has the tendency to follow Ryoma around, even to America by slipping into his tennis bag.
Ryoma's older half-brother. Their relationship as brothers is quite unknown but in Futari no Samurai, Ryoga often calls Ryoma weak when they play tennis when they were young. He currently sees Ryoma as his rival and tells him to dream higher at the end of the film. He is shown to care for Ryoma and has saved Ryoma from attacks. Ryoga has mentioned that Ryoma used to worship him when they were kids. He also mentioned that Ryoma used to call him 'nii-san' and stuck to him like glue. Ryoma vehemently denied it, though the blush on his face implied otherwise.
The Seigaku RegularsEdit
Ryoma has a good friendship with his fellow regulars, and deeply respects them even when he tends to provoke them. The other regulars also care about Ryoma since he is the youngest among the regulars. When he is always late for tennis practice and gets into trouble before or in the middle of the match they are still there for him and ready to cheer him on to victory. Out of all of them, he is closest to Takeshi Momoshiro whom he often hangs out and makes trouble with.
Ryoma and Kintarou often argue over tennis and outside of it. Ryoma is usually annoyed by Kintaro's high energy, but Kintarou sees Ryoma as a rival. The two don't get along, but they both share some common things like challenging players who are stronger than themselves. They also have a poor sense of teamwork which Ryoma agrees to (during the Mountain training). Kintarou does show he cares about Ryoma. He always demands to have a match with Ryoma and calls him 'Koshimae' as an alternate way of reading his last name. Ryoma is often exhausted by Kintarou's loud and brash personality and wishes to be left alone. Of course, Kintarou never complies.
Ryoma and Kazuya seem to share a rivalry similar to what Ryoma and Tezuka have during their time in Seigaku. Kazuya seems to make Ryoma aim higher than his current skill level. Kazuya takes on the role of Ryoma's mentor at the U-17 camp. It was stated in the New Prince of Tennis Fanbook 10.5 that Tokugawa had always wanted a younger brother and therefore took a liking to Ryoma. However, since his favorite Ryoma became more attentive to Echizen Ryoga, a burning sense of rivalry with Ryoga had developed.
Sakuno is the first person to have met Ryoma in both the anime and manga and has grown to admire him. She is inspired by Ryoma's tennis and decides to take up tennis herself. She and her best friend Tomoka Osakada both go to his matches to cheer for him. Ryoma is unaware of Sakuno's feelings for him, though he is shown to have protected her from bullies at times (mostly unknowingly).