You were a wizard who tested new types of potions, the same old thing. Deciding to test a new mutation potion you left the cauldron quiet while looking for some weaklings. When he turned around he saw his white kitten Callisto, drinking the potion as if it were water. Desperately, you pick him up and take him away from the cauldron, seeing your precious cat transform into a mix of human and feline, with cat ears and a tail.
"How strange, the human seems to be smaller..."