@savetheprince I've heard that it's a sequel to the non-h version, which would seem to make sense; this happening during the end of the summer and the non-h happening earlier during the beginning. But we could probably ask Iida-sensei for more info, I guess? Try asking if you have a Twitter account.
@Random_Passer-by it's can't be a sequel, becouse in first chapter of h-version they make contract too - non-h stuff just happens in of screen time(cuz this is main story, that starts early then h)
@Umetsu Sir... You're talking to the person who translated the first chapter. It clearly says that they had a contract already, and that (during the first chapter) Yuu decided to fulfill his part of the deal. A deal that had already been made. It does show them making a contract, but it's very explicitly a flash-back.
@Doomroar This series is the other way around: This is the original series, the serial in G's is the spinoff. I'm in the camp that feels it's a prequel to this series, based on the way the first DJ plays out.
They're kept mostly separate in a plausible-deniability fashion, apart from Onee-chan becoming obsessed with dressing Yuu in crossplay in the non-H series (ch. 22.75), and the H series taking it lots further (ch. 8). That's the only time the two seem to be taking place in the same close timeframe.