To be honest, the only in common with Rainbow City is the zombie outbreak so idk if it'll be what you're looking for, but I liked Believe my sign<3
If you tell me what exactly you're looking for maybe I'll have more recs!
For zombie apocalypse try "Dead man switch"
Not sure .... But maybe Radio Storm?
LITTLE MUSHROOM IS PEAK OMG ITS SO GOOD!
Wait, I've started Little Mushroom and I think I understand now what you meant. Not the same graphic quality, but check dear 00 by Brothers without a tomorrow. This one was the first in my mind when I started reading Little Mushroom
anything like little mushroom and/or rainbow city?