Syusuke Fuji/Relationships

Yuta Fuji
Fuji loves his younger brother very much, and has been incredibly protective over him ever since they were little. Initially, Yuta seemed to dislike his brother and would often act irritated or agitated once compared to him (which was a very common occurrence). He developed a complex due to the fact that people would always see him as "Fuji's little brother" and nothing more. Fuji, however, remained loving towards his brother, despite everything. He would often tease him once the opportunity would present itself. While Yuta does still act somewhat cold, he does in fact care deeply for his brother, he just has trouble showing it.

Yumiko Fuji
Yumiko is rarely seen in the anime, but from what we've seen, she cares deeply for both of her brothers. She's very supportive of them and enjoys teasing them. She's quite popular among Fuji's and Yuta's peers.

Kunimitsu Tezuka
Tezuka and Fuji have been very close friends since they were first years. Fuji sees Tezuka as his rival in tennis, having even skills against each other. He really values his friendship with Tezuka. When Tezuka left the U-17 Training Camp for Germany — after losing to him — Fuji shed tears, not for his loss in tennis but for the final farewell to his closest friend. Tezuka was almost never seen without Fuji when they were in Seigaku, and it's shown that Fuji is one of the few people who can bring Tezuka to smile.

Kikumaru, Oishi, Inui, and Kawamura
Fuji has a good relationship with his fellow seniors, knowing them since their first year. He is occasional Doubles partners with Kikumaru and Kawamura, and shares the same class and is seatmates with Kikumaru. Fuji and Inui are also on good terms, the former being the only one who actually enjoys the latter's somewhat horrible vegetable juice. He also respects Oishi, who is Tezuka's secondary.

Ryoma, Momoshiro, Kaido, and freshmen trio
As a senior, Fuji cares for the younger members of the team, despite the usual provoking he does to them. Ryoma and Fuji have quite the rivalry, and has played him against his own limits. He also seems to treat him like his little brother (the fact that he's the youngest on the team). Fuji also seems to be able to keep Kaido and Momo in control. He is also on good terms with them and occasionally has friendly matches with them. Fuji gets along with the other freshmen members as well.

Yukimura and Shiraishi
The three of them get along very well as they share similar interests. They often bond over their favorite plants (Fuji's love for cacti, Yukimura's for flowers, and Shiraishi's for poisonous plants) and discuss why they love their preferred plant so much. They also seem to respect each other, not only as individuals, but as tennis players as well.