Need help moving forward

Ive been playing for a while now but really i suck. Ive never gotten a key, my towers level one and my best character is miku nakano(the goat) ranked at #16. Recently ive tried doing things to be better but id like some more help please.

How do i increase my chance of getting keys? How do i earn kakera faster? Anything else i should know?

Please and thankyou for your assistance