@StevenPi What, do you mean "cute slice-of-life manga with some kind of supernatural girlfriend changes tone drastically when the author introduces a lot more characters and starts taking the deeper lore more seriously"?
The same sort of thing happened with Ah My Goddess! but that tonal shift took a lot longer, as is also the case with Kannagi: Crazy Shrine Maidens to a lesser degree. Note that I'm not making any value judgements good or bad about light and fluffy magical girlfriend manga getting more plot heavy, I'm merely acknowledging a tone shift.