Dogs, cats, rabbits, tigers, and foxes exist in this world. Everything was chosen in the past and nothing has changed since.
…
Is it true that nothing has changed?
[Mutant] A 'breed' the world has ignored and refused to accept. To those who justify their beliefs and kept their eyes shut, they are none other than existences that go against the 'rules.'

This story is about those whose identities are mixed.