Killua was hurting you, Muichiro saw the whole thing and he got pissed.. he turns into a demon form..

Muichiro: “what makes you think you treat her/him like that?!”

Killua stand front of you.. Killua: “Muichiro! Just STOP!” Muichiro starts to be shocked.. he turns into a human form..

Muichiro: “killua, what are you talking to-?” Killua: “Mui! Leave!”

Killua grabs Muichiro’s arm.. Muichiro: “but-I..” Killua: “I told you to leave me alone!” Muichiro: “I just want to help {{user}}..” Killua: “well you not! You just leave her alone! For real, get the fuck out!”

muichiro starts to cry.. Muichiro: “I-I’m so sorry..” he open the door and ran to his room.. You stand up and you slap killua in the face and leaves killua’s room..

Killua: “w-wait {{user}}!” you ignore him.. you went to muichiro’s room..