Hi I want bl like little mushroom and rainbow city

Try Radio Storm, it's the most similar imo.
If you like Fantasy then I highly recommend Traces of the Sun as well!

OMGGGG EEEEEE YOU MY FAVVVV NOW TEEHEE I LOB RAINBOSSI AND LIL MUSH
but seriously, that’s impossible. There’s no other BL on this earth that can come close to what these two have, I’m willing to fight people over this. Anyways try “thrive in catastrophe” on manhuahot. That’s their secret love child >.<