This arc is about the relationship between Sir Nighteye and All-Might, and their differing views of what a hero is. Especially with Nighteye as his power basically has self-fulfilled to his views. He won't listen to rationality and relies too much on his quirk. It has literally pushed Nighteye away from what made All-Might such an amazing hero and why others dawdled behind. The entire arc examines how Nighteye and All-Might have proteges who both exhibit amazing quirks and the termperment to be heroes. It has nothing to do with Eri being a "little girl". It has everything to do with them stepping away from being "a hero" for a second to be the cautious one, and how it runs counter to everything they have ever been to that point.
