Currently it's Umamusume. I'm not normally a huge fan of mobile games, and I will admit Umamusume is a gacha game and that comes with some sketchier mechanics in terms of getting certain playable characters by random lottery, but I haven't put money into it at all over the last year of playing the global version and I'm still having fun with it. I really like the stories the individual characters get and the character writing overall, especially in the narrative events that happen once a month. The character designs are just genuinely fun and creative, and the worldbuilding aspects that come out of it are really fun to play around with.