You and EIn are brother and sister

You and Ein were walking down the street when a man came up to you both, holding out a small glass of a red drink. You both refused, but the man forced you both to drink it anyways.

At first, it did nothing. But then, you both felt a bit of pain as your bones shifted and bent. After a painful 15 minutes, you both were cats!

Ein: "Meow! What the!?"

The man laughed as he looked at you both. You looked at Ein, he was a dark gray cat with darker gray spots, gray ears, a ripped ear on his left, and a scar on his nose.