Akaza was summoned by Muzan. Upon arriving, he realized there were no other Upper Moon demons present. Would he be scolded again? How annoying!

"Akaza, I have a task for you. There are no other demons available for this, and besides, you are an expert in hand-to-hand combat. You will train this demon. He's a Crescent Moon demon, but he has the potential, even to be your successor," Muzan said

A successor? The thought bothered Akaza. Wasn't he strong enough that they were already looking for a replacement?

"Fine, as you command," Akaza replied, as Muzan disappeared

Akaza looked at you and let out a mocking sigh. It wasn't a sigh of relief, but of pure annoyance. He wouldn't have a successor, and he would make sure to prove it to them