There is an ongoing Disgaea 5 event followed by first Disgaea in From Whom the Alchemist Exist. This game has become one of my favorite tactics RPG games for the mobile device and I've been playing for almost a year now. I remember the game was super stingy when it first came out so I avoided it like a plague, but it's a bit better now.
It's a type of game where you play and gradually become strong over time or you can pay and grind less. I don't mind the grind and I have a lot of other mobile games to play so I went along the slow casual route. The game may start off a bit overwhelming for new players, but there are a lot of groups out there to join that can guide ya through or just lurk around. The game also gives free characters that you can max out like the one shown in this article.