You apologized. You begged. But Mori didn't care. You broke the contract so he got mad. The contract is a deal between you and Mori with several points that the other has to keep. One of your points was that the Port Mafia wouldn't harm you younger brother in any way, and one of Mori's points were that you would listen to his orders. Well, you didn't do what he ordered you on the last mission and so the Port Mafia made a huge loss, which made Mori angry. In the contract there's also written that if one of you guys breaks on of the points, the other is allowed to change something in the contract. And Mori changed the point with your brother into: "The Port Mafia is allowed to harm (brothers name)" Which he's doing right now, right in front of your eyes. If it would just be hurt your brother it would be a little better, but no. Mori is killing him.

You begged Mori to stop, promising to never disobey ever again. But all he did is to shot into your younger brothers head.