And one of the biggest wank sources in the fandom? How the fan-made Tezuka x Fuji couple got quite more fanservice in both manga and anime than other couples. Three-episodes anime match chock full of typically shoujo symbolism, like Cherry Blossoms and Together Umbrella? Check. Said match finished by Tezuka and Fuji practically hugging and smiling? Check. Manga match between Fuji and Niou where he sees Niou as Tezuka? Check. Fuji kinda flirting with Tezuka after the finals? Check. Tezuka smiling at Fuji and asking him to not tell anybody? Check. Inui saying Tezuka's "so naive" in a tone that sounds almost like he's their fanboy? Check.
The image songs make some duets sound just So. So. GAY. Inui and Yanagi's duet is all about them being reunited after years and planning to take over the world together, in example. Makes some sense in the context of both being the Genius Bruiser type, but still...
Oishi and Kikumaru are another popular slash pairing because they play doubles together. They obviously care for each other as partners and it can easily be interperted as a romantic relationship. Same goes for Ohtori and Shishido, also Niou and Yagyuu.
In fact, those late-night "training sessions" with Ohtori and Shishido are played up to the nth degree in the anime for various imaginations of the fangirls
And let's not get even started on the musicals...
And the fact that Smash Hit 2 actually takes the time to NAME the pairings...
Ryoma and Momo are often slashed together as well. They are very good friends in the show and hang out a lot.
In the fanbooks, Oshitari Yuushi and Mukahi Gakuto's meeting has all the implications of a shoujo manga and more
Sanada and Atobe attending a tango concert together, and somehow managing to sit right near each other, and having the tune of the concert stuck in their head. It's just a mass of implications.
Also Sanada's devotion towards Yukimura reaches very high levels. Parodied in two scenes of one of the Chibi-family episodes.
Also Tenimyu doesn't help to prove wrong, because all of their duets and setups came close to love song tune.