I believe that project sekai should add a trading feature. We could add a chat so less scamming could happen. Also I don’t think there are people that would try to scam on project sekai. This would be very beneficial for players that have un-used cards or cards they don’t want. Take this for example, we have person A and person B. 

person A: ugh! I have this Toya card I don’t want!

person B: omg!! I’m so jealous!! I wanted Toya so bad! I got Rui!

person A: omg I wanted Rui!

*they trade cards and everyone is happy *

We can add limits to this, I’m not sure what kind of limits but maybe that you can’t trade a 2 star for a 4 star.  If you’re trading 4 stars then either you don’t level the cards or you both level the cards. We can also add rank limit. It can’t be a rank 1 player trading with a rank 140 player. You have to at least be rank 50 to trade. We can also make it so you have to spend crystals to trade and you need to have the other person friended to trade.