Umamusume: Pretty Derby

Probably my favorite gacha I've tried. The character stories are well-written and include lots of little details taken from the stories of real racehorses, which gives them a lot of depth and stories that sometimes go in an unexpected direction. The game mechanics are easy to learn, hard to master - it doesn't take a lot of work to clear the career mode but if you try PvP then you'll find there's some real depth to the race mechanics and planning your career. Each turn of the game plays quickly, which makes it easy to lose a lot of time to "just one more turn." And most importantly, the races are exciting - the mechanics do a good job of making things feel tense even when your girl is the favorite, and there's always some uncertainty even when you do everything right. And the winning concerts are - okay, the concept sounds like the goofiest thing ever, but it is genuinely really satisfying to see your girl on stage after a hard-fought victory. As for the gacha mechanics, well, gachas are inherently evil but this one is tolerable. You need to split your spending between new characters (and since each character has their own career, it's basically buying new stories), and "support cards", which are side characters who help you train. Support cards don't look flashy, but you really, really need them if you want to get good results from training, so be sure to save some carats for them. The gacha only has a hard pity system - if you pull 200 times on a banner without getting it, you can get one of the characters for free. If you pull less than that, no prizes. So the game heavily rewards saving up, skipping banners you can't afford and spending big on the ones you really want. Check online for what banners are coming up - the Japanese server is years ahead of us, so there's plenty of information on what stuff is worth buying.