Twitter. Pretty much my default app, honestly. I'm pretty much always checking the app when I can't be on website Twitter at the time.
Love Live! School Idol Festival (Japanese) - do I even need to explain it's a japanese idol game.
...Which are the only apps I really use on my main phone that isn't built into the system.
As for my deactivated gaming phone.
(All Japanese idol games/raising sims btw)
Ensemble Stars (Taiwanese), A3!, Band Yarouze!, Ensemble Girls, IDOLiSH7 and Dream Festival!
Yes, I know that's a lot.