this manga is so fricking brain dead. Why would you let your baby brother go into a mine with poison gas at any point? That's just dumb. Much less with someone who was basically an acquaintance with her at that point.
Bro, that just chilling and he frickin hit him. (most) Sharks don't even see humans as food. He prob just wanted to take a nibble.
Sharks aren't evil. Stop the discrimination.