The Strongest and Fastest Unlimited Level Up: With the Skills [1000x Exp] and [Level Free], I Broke the Upper Level Limit and Rose to the Top! - Ch. …

[MangaDex]

 

[lesseffective]

The most destructive force imaginable -- calling a girl by her first name when she's not prepared.

 

[monkey123]

I never understand how those Japanese go poof because of first names!

 

[PLaci1982]

Seems like this was one plot from the other group members to bully the girl, with forcing the MC to call her by her 1st name.

I never understand how those Japanese go poof because of first names!

Seems like calling the other by they 1st name is considered intimate. Like when you are (close) family members, good friends, or lovers. And that girl is mad into the MC.