Personally, I think it'd be hard to do w/ the source material, cuz it's basically joining an adventurer guild and completing quests, later on there are guild tourneys, but that's about it. Though, I think you could use the alternate dimension bit and guild tourney to make something similar to a management simulator.
Or you could spin it as a brothel instead.
TL;DR: Basically, Fairy Tail, imo = a simulator/management style game.
Another way would be from near the start, there's a ring that can charm people, so maybe you discover a more powerful version. *Shrugs*
Someone speculated that time frame, due to the mentioned 2 scenes per month.