Karupin (カルピン Karupin) (Kalpin in the English Dub) is a himalayan cat owned by the Echizen family which Ryoma loves and is very attached to. Karupin is just as attached to Ryoma.
Karupin is often seen sleeping or just roaming around the Echizen household. He is mostly seen in Ryoma's bedroom sleeping together with him. Karupin is also seen to be very mischievous and quite smart in episode 27 as he was aware that Ryoma has accidentally packed his favorite toy and even followed Ryoma to school.
This caused Ryoma to be worried and he started looking for him around the neighborhood. Karupin was found and returned by Momoshiro and the Seigaku regulars (Tezuka, Oishi, and Kikumaru) in the end. When Ryoma was invited to play in the USA Open, Karupin hides inside Ryoma's bags and followed Ryoma to America.
Ryoma Echizen - Ryoma deeply loves Karupin more than anything else (minus tennis). Karupin is also deeply attached to Ryoma as well. Despite the mischief and trouble, in the end Ryoma still finds himself forgiving Karupin.
Nanjirō Echizen - Nanjiroh and Karupin do not seem to get along. They are often seen fighting with each other. Karupin is not very fond with Nanjiroh either as he is always seem to attacking him like biting, scratching him or destroying Nanjiroh's magazines.
Nanako Meino - Nanako cares about Karupin just much as Ryoma does. She is the one who takes care of Karupin when Ryoma is at school or attending a tennis tournament. Karupin seem to love her back.
Kaidoh Kaoru - Karupin seems to enjoy Kaidoh, always wanting to play with him whenever they see each other. Kaidoh also seem to enjoy playing with Karupin.
- Favorite Things: Cat Toys
- Favorite Food: Kitty Snacks
- Special Skill: Backfoot Kitty Kick
- The Prince of Tennis mangaka, Takeshi Konomi, owns a cat named Kahluamilk whom he uses to assist him in drawing Karupin.