Name: Echizen Nanjirou
Occupation: Former tennis pro, monk
Special moves: Nitouryuu
Basic information:
Though nothing much but the eyes look alike, Nanjirou is Ryouma's father, the legendary Japanese tennis pro who surprised the world. He definitely is still young, but there has never been a reason given to explain why he retired so early. At present, he is simply a monk whose work is to just ring the temple bell as he reads his favorite girl magazines. Though he's someone his age already, Nanjirou acts like a young playful, and perverted as well, kid who bluntly shows the fact that he loves pretty girls by trying to flirt with them straight on. We also don't see him play tennis with anyone else besides Ryouma, whom he really hopes will one day surpass and defeat him. Even though Nanjirou's his own father, Ryouma never fails to behave sarcastically, just like always, but Nanjirou knows his own son too well to be bothered. In fact, he loves teasing and making fun of him instead!

Name: Nanako
Occupation: ---
Basic information:
Nanako is Ryouma's cousin whom we see cooking his breakfast everyday and giving him words of support and encouragement, especially before a tournament. She is also against Nanjirou reading his perverted magazines and is probably the only one who really does the work around their house.

Name: Inoue Mamoru
Occupation: Monthly Tennis Magazine reporter/journalist
Basic information:
Inoue works for the Monthly Tennis Magazine company and is always going from place to place to check out the tennis players of various schools, and interviewing them. Of course, he mostly sets his eyes on Seigaku and never fails to be there to witness their exciting matches against not only rival schools, but against themselves during ranking matches and other events as well. While watching by the side outside the court, Inoue often acts as the commentator who does the explaining of certain moves, problems, solutions, etc that occur during the matches. To put it simply, Inoue is a very supportive tennis enthusiast.

Name: Shiba Saori
Occupation: Monthy Tennis Magazine reporter/journalist
Basic information:
Shiba is a junior to Inoue and is mostly seen around with him. She is usually the one to bring the camera/video camera to record and/or take pictures of the match. She is only still around her early twenties but is, like Inoue, a really big fan of tennis and everyone of the regulars in Seigaku. While Inoue does the explaining during a match, Shiba does the questioning.

Name: Fuji Yumiko
Occupation:
Basic information:
Yumiko is Fuji and Yuuta's elder sister and only until recently is her face revealed to us. She is not really familiar with tennis but she definitely knows a lot about her own brothers and adores them just as much.

Name: Karupin
Basic information:
Karupin is Ryouma's playful and curious cat. He really loves cat tails (a type of plant), especially the cat tail toy that Ryouma bought for him. While following Ryouma for that toy that fell into Ryouma's bag, Karupin wound himself up in school where he met Kaidou and some of the rest for the first time. He also gets to sleep in Ryouma's bed, and even under the blanket with him. What a happy cat.

Name: Sasabe
Occupation: High school tennis player
Special moves: Bullet serve
Basic information:
Sasabe appears in Prince of Tennis's very first episode. He is a 16 year old high schooler and used to enter the Under-16 tennis tournament where he met Ryouma and experienced the shock of his life. He is the typical arrogant bully and the son of a rich man.

Name:
Occupation:
Special moves:
Basic information:
This man is Sasabe's father, equally arrogant and shameless. In Tennis, he is called the Golden Retriever. Besides tennis, he and his son also play beach volleyball, but as always love to use dirty tricks.
(Please pardon me for forgetting his name.)