I need help on the show Gungrave please.

Well to answer your questions I think the person that gets killed is just a random guy. It's in the second episode when they show Brandon and Harry as young punks, not like in the first when they're older. And I believe it's called young dogs, I'm not certain but I think that's right. Brandon says the quote too incase your wondering.

*spoliers I guess*

"2 questions.

1: Who was killed before the quote "Like and death are 2 sides of the same coin.""

That would be the brother of "Mad Dog", I believe the brothers name was Deed or something, the one leader of the gang that they always fought against.
From memory the full qoute is something like:

Harry: "No, I will not take away from you, instead I will give you, and that gift.... is death!" *kills Deed*
Brandon (Narative): "Life and Death are like two sides of a coin, the ability to give, and the ability to take away, and the choice we all have falls over us all like this rain...."

2: What is the # and the name of the episode that quote was said on? Thank you.

That would be episode 3: Rain I believe, gonna check on my facts real quick and post if anything was wrong.