... I have so many theories on this that it's hard for me to pick just one to tell you here. XD;;; I think I'm going to go with my standard shtick though, just 'coz it's easiest. XD;

Ryoma loses his virginity to Atobe after they play in Nationals (though he may or may not have performed sexual favours for other people before this point, for the sake of this meme, I'm referring to penetrative sex as what qualifies for loss of virginity). He considers it one of the most challenging, mentally stimulating games he's ever played, and, in the end, what excites Ryoma and gets his attention is someone who can play on the same level with him in tennis. After the game, he is surprised Atobe held through with his promise (and a little disappointed when he doesn't get to shave Atobe's head himself), and while he's off guard, Atobe uses some stupid and probably tennis-related pickup line on him. Ryoma smirks and says something cocky, but is internally delighted that Atobe is seeing him for him and not obsessing over Tezuka, and so he accepts and spends that night at Atobe's. He goes with the intention of semeing but that falls through somewhere along the line, and pretends that he's not a virgin even though it's really obvious that he is. Afterwards, he somehow keeps it from Tezuka, who finds out much late (as in this fic) and flips out.

...wow, I almost did both of the memes in one. XD;;;; I'm not counting it as the second one though, but... there you go. XD;;;

And please do do more later :D