One Piece ~ Because without Zoro, Luffy would have been dead a long time ago. EVERY TIME( and that is literal) Luffy has fallen into the ocean Zoro, without thinking, without hesitation would jump in after his captain. and that is a true Nakama
By far the saddest arc in One Piece. It completely broke me the first time I saw it. Up until this point, no one had ever died in One Piece, not even bad guys. To lose Ace, and see Luffy so broken.it ripped my heart in two.