Now that i think of it couldnt the whole fairy trainer be simply revamped with a different story and names whilst still having all the characters and work to a certain extent remain intact? Like they were transported somewhere, figuring it out, starting anew bla bla bla other plot points and what not, essentially making it some sort of mystery isekai with fairy tail or perhaps even some original characters or from other anime, like what isekai quartet did. We can still have the same male mc with the same cast of characters and scenes of course they will be tweaked to fit in the new story but essentially most of the work is already there.
From this we can also have some cool game elements like choosing sides, balancing powers so one does not end up annihilating other, some managing stuff with resources areas that would come under attack bla bla theres quite a lot you could add in it
