@Shuzuchi So because they know the other girl is strong and a powerful attack was launched at the both of them and couldn't stop and the main girl clung to him to not get injured is bad?
@MadParadox I'm guessing it's a technique taught by elder Mu. That's why he didn't want to use it and accepted defeat, because it's probably too powerful and Mu probably told him to only use it when really necessary.
Not sure though, next chapter we will be more clear.