Answer:
I am sometimes referred to as chips
My first is in fish but no in snail. My second is in rabbit but not in tail. My third is in up but not in down. My fourth is in tiara but not in crown. My fifth is in tree you plainly see. My whole a food for you and me.
I'm a ruler with 12 agents. Half of them work in the darkness. Who am I?
Without me everyone would lose their head.
What gets sharper the more you use it?
A little house full of meat, no door to go in and eat.