Souji Ike, also known as Sou-Chan, is a professional tennis player who was previously a member of Southern Tennis Club, STC. He was introduced to tennis by Natsu Takasaki and quickly surpassed her and players of his age. Souji is ranked in the top 10 in Japan. (Source: Baby Steps Wikia)
Takahashi Kousuke was the top seed in the All Japan Tournament during his 3rd year high school. He was the semi finalist in the tournament which was later won by Yu Nabae. (Source: Baby Steps Wiki)
Megumi Nakajou is a very skilled tennis player. She won the All-Japan in middle school and is a freshman high schooler. Megumi is very skilled and was able to trouble Natsu by not letting her settle down. She is said to have a somewhat odd style of tennis. (Source: Baby Steps Wikia)
Ryou Oobayashi is one of the top seeded players in Kanagawa Prefecture. He was Eiichirou Maruo's first official opponent in a tournament match. (Source: Baby Steps Wikia)
Sakakibara is an ex-professional tennis player and a newly appointed coach at Southern Tennis Club. She supervises the female players in STC. She was appointed along with Ryuhei Aoi. (Source: Baby Steps Wiki)
Masumi Makihara is one of the female players at Southern Tennis Club. She is friends with Natsu Takasaki and Hana Yokoyama. She is a regular Kantou Tournament tennis player. (Source: Baby Steps Wiki)
Takuya Miyagawa is one of the top players in Kanagawa prefecture, but his All Japan seeding is not very high. He and Ryou Oobayashi used to go to same school. (Source: Baby Steps Wikia)