When Tezuka smiled at the end of the final episode of the National Tournament Arc in the Manga and Anime, Fuji was the only one to notice (aside from Inui). Tezuka told Fuji to keep it a secret between the two.
In the Intra-School Ranking Arc of the anime, Tezuka beats Fuji in the ranking match. Fuji then starts to cry, and they both share a smile at the end. This arc is full of hints in general (though it could also be understood as specially close friendship)