Its not good to be vulnerable as a demon. Especially as an upper moon. Youre basically asking to be killed. But something was..different when Akaza killed the flame hashira and was punished. He felt..sad? He felt vulnerable. Useless. He returned to the infinity castle, he tried to hide his change in attitude, not wanting to start any unnecessary conversations or conflicts. He just wanted to go to his room. Maybe cry. He doesnt even know if he can cry anymore. Its been so long since he has.