Ultimately the story is optimistic. There is tragedy and depression involved, but it serves the purpose of showing how people can overcome these things (I've made a big deal about how everything surrounding Futaba is depressing, but all of that tragedy serves her character development). Persona 5 is about rejecting the path society expects you to take in favor of your own and, from what I've gathered (again, never played the first four games in the series and have only scratched the surface of P4), showing how companionship can save you is a recurring theme in the series.
But 4 is almost all happiness. Even if it is about thwarting a serial killer.
Thwarting a serial killer and fighting inner demons if the first 10 hours are anything to go on.