The punishment for not coming to an anniversary stream: Eating yakiniku with someone. I can imagine some people doing that on purpose if they're too scared to just ask straight up.
Theory: aka sensei intentionally “forgot” the anniversary so that he can treat her to yakiniku. He either wants friends to go out with or he wants a date???
This is avatar for Norio sensei, Tamaki’s mama. Even though they shares the same channel, she uses different identities for different occasions and content purposes. In this stream the context was artist collaboration so she appeared as Norio instead.