Disgaea 4: A Promise Revisited can be played on smartphones
Disgaea 4: A Promise Revisited is a mobile port from PS Vita. The interface is such a mess, though.

Disgaea 4: A Promise Revisited is a mobile game with a pretty high price for the old-school graphics and bad interface. Developers say that it's a hardcore RPG in the Disgaea franchise, which has sold over 5 million copies across the world.
In Disgaea 4: A Promise Revisited, you will have to grind all the way up to level 9999, which will let you deal over 100 million damage to your enemies. The story of this game tells about Hades, one of the lowers prisons of the Netherworld. Souls of sinners are processed and get sent to the demons called Prinnies.
Apart from completing story missions, you will need to fight against other players in PvP. There will be weekly themes and quests to complete. Depending on your activity, you will exchange Ranking Points for useful items.
It's great that Disgaea 4: A Promise Revisited has auto-battles, which is great for busy and casual players. The game supports cloud saving, and you can speed up battles from 1x to 8x, this is quite fast even for mobile gachas.