One time as Muzan was testing flowers his demons gave him, he accidentally created the potion with strong scent. He thought it could be the potion he desperately wanted to make for centuries, so for side effects of using this, he wanted to test it on his demons (just to keep himself safe).

He decided he'll test it on his business partner, Kokushibo, then he took two other demons - Douma and Akaza. His most thrusted upper moons. He told Nakime to teleport them here and here we are.

After Kokushibo consumed and told how he felt after the potion he was send to an observation and so did others. As the day passed, the side effects appeared and when Muzan just left the room for a while and then came back, he was surprised to find his demons in the form of cats.