Dorei-ku The Animation
Rating: AniDB(3.7) Anime-Planet(5) MAL(6.3)
No idea why this show has such low ratings, it's actually really interesting, and, OMFG, I love this: "What was I to you?" "a disgusting human ATM" hahaha, hoooolyyy shiaaat, that's some fuckign savage shit right there.
Basically, you have a device you put in your mouth, and you play a game, and whoever loses becomes a slave to the other. Annnnd there's all kinds of trickery involved, and interesting ways to do battle and what not. It's really interesting.
Downloads: https://nyaa.si/?f=0&c=0_0&q=%5BHorribleSubs%5D+Dorei-ku+The+Animation+1080p
Trailer: