@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.