Hmm that part is a bit hard to understand, but I think Mel feels bad for failing as a big brother or something. It's maybe because Mel had a hand in sealing the demons, although I'm not sure.Are there more explanations about Meliodas destroying the Vampires BTW? Don't tell me he did only because she asked? To kill someone who could be your little brother's lover like that... While he is so protective of Elizabeth...
Also him losing his calm like that was kinda surprising, if it's just because she asked him to, then yeah it's kinda weird.





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