Increasing chance on UR drops
What i have been experiencing so far, is that it looks like drop rates are connected for all the vans. So i just save some common keys and try opening them before going onto premium. If i have my "luck" i will get something cool from commons -> i am most likely getting something cool from premium keys.
Now, I am not 100% positive this is true, but so far worked me. Tried it only 3 times tho.
Used 1 common key, got Mikako [R] -> Got my first UR with premium key and some SR and R
Used 4 common keys and got 4 commons -> Got "just" 4 Rares from premium
Used 4 common keys, got 1 R, 2 UC, 1 C -> Used 4 premium keys, got Gwen and Chikara (probably 2 strongest characters in game lol, what a luck) + 1 SR and 1 R
Honestly, so far it seems like it might just work, but i still need to do some testing, because 3 times isnt enough. Just thought i would share this so others can try it aswell.