Red Son

Just look at them! Their faces speak for them!

Firstly we have Mei who looks really surprised to see Red Son not yelling or being a chaotic mess. He's just worried about his dad, you know, like a human, like a son who loves his parent. She's realizing that demon has life, thoughts and feelings other than destroying and killing. That he can love or be hurt.

And after that moment she stops being suspicious about him and starts to trust him and help him.

And on the other hand, Red Son is surprised to see someone stops and actually listens to him.

He is so confused that Mei says nothing, just stands and listens. That is the very first time someone gives him a little bit of selfless attention. He begged for the attention for such a long time without any results, he's so confused when he already gets it from a stranger/enemy girl.

And since then, he stops using the word "peasants", he stops trying so hard to be the leader and to have everyone's attention. He's more in the background. He becomes a little bit more humble.

It was only a few second of silence, but they both change a lot.

Mei from being violent and suspicious:

To being supportive and caring:

And Red Son from playing hero for being in the center:

To being an actual hero by helping in the background:

Conclusion? Well, you can call it "over-analyze", but hear me out! It's not only about their bonding. It's about Red Son becoming a hero after realizing that to gets someone's attention and respect he has to be true himself. It's about Mei realizing that even a demon is a person, even an enemy has feelings, that people who hurt also can love and be hurt. She forgave him and he grew humble and true.