The two ongoing manga I'm reading that can be considered fantasy are
>Saihate no Solte
>Mondai Darake no Mahoutsukai
The second one is an isekai and so far, while having a somewhat interesting premise, really hasn't gone anywhere very interesting yet. I'm only really reading it because it's by the guy that did Yugami-kun Has no Friends. The chapters so far have been free though, so that's nice. Saihate no Solte chapters are free too actually, though I think there's a wait until they become free and then they at some point later stop being free.