This app was mentioned in 5 comments, with an average of 2.40 upvotes
https://play.google.com/store/apps/details?id=air.com.lunimobi.animegacha
https://play.google.com/store/apps/details?id=air.com.lunime.nekogacha
https://play.google.com/store/apps/details?id=air.com.lunime.gachaclub
https://play.google.com/store/apps/details?id=air.com.lunime.gacharesort
https://play.google.com/store/apps/details?id=air.com.lunime.gachaverse
Anime Gacha!: https://play.google.com/store/apps/details?id=air.com.lunimobi.animegacha Size: 29 MB
This is pretty simple...its basically a Gacha simulator with RPG elements where you collect little toy capsule things called Gacha and fight "monsters" with them; but its as simple as tapping their portraits to attack the one enemy in their way. And the game is so simple, Its offline and devoid of IAPs. You can also collect as many Gacha(s) as you want with the little slot machine since you never run out of gacha tickets. There's absolutely nothing to spend but your time.
If he doesn't mind loud noises and finds 420blazeit Illuminati SANEC funny, there's MLG Bird. Which is basically Flappy bird on Mountain Dew and Dubstep....or he could just turn down the volume; that works too...hectic fun btw. Size: 23.50 MB
http://www.amazon.com/Random-Noobs-MLG-Bird/dp/B00NLQR98Q
Retro Star Wars: https://play.google.com/store/apps/details?id=ca.pocketguru.retrowars Size: 11 MB
Its an arcade shoot'emup where you control an X-Wing in first person with Wireframe 3d graphics. Hopefully dodging obstacles and shooting TIE Fighters isn't too much thinking.
Anime Gacha - https://play.google.com/store/apps/details?id=air.com.lunimobi.animegacha
I personally think this is more of a Gacha simulator than a Gacha game, though there is an RPG mode where your Gacha's strength scales with the number of times you caught it. The game has infinite tickets where you start at 10 per play but its more for the sake of a Highscore competition that's relevant to how often you get higher ranking Gacha.
The game's IAP is just a permanent doubler if you want to speed up your Gacha's leveling by giving 2 Gacha worth of the one you caught.