Will someone else be able to become Pirate King other than Luffy? No.
Will someone else other than Nami be able to draw a world map? No.
Will someone else manage to become a brave warrior from a coward? No.
Will someone else manage to find the All Blue other than Sanjino? No.
Will someone else manage to build a greater ship than Franky? No.
Will someone else other than Chopper find a cure for any disease? No.
Will someone else other than Brook fulfill the promise of Rumbar Pirates? No.
Will someone else be able to steer a ship better than first son of the sea? No.
Will someone else manage to uncover the true history instead of Robin? No.
Will someone else be able to beat Mihawk, other than Zoro?