Aah, the cards and pieces (in the garage) are for the game. Like life itself, it's all meaningless, but you can choose to perceive meaning in the cards. Also, they earn Jpops, just in case you want more.

((like life itself)) lols xD
and one more, what's karma about?

I'm not sure exactly, but it's basically like Reddit karma. You get it for doing certain things and getting upvotes, and it can't be spent or anything.