Lin Ye, a young man from the modern world, unexpectedly transmigrates to the world of One Piece and wakes up in Foosha Village in the East Blue. After a chance clash, he and young Luffy become friends through a fight. They share a desire to become stronger and go on freewheeling adventures, and Luffy excitedly grabs him and shouts, “You should be my brother too! Let's become pirates together!” And so Lin Ye begins a journey alongside the future captain of the Straw Hat Pirates.
As someone who knows the story, Lin Ye doesn't try to change the main plot. Instead, he chooses his own way of protecting their adventure: he warns Luffy about certain traps in advance, while leaving him challenges that help his companions grow. Thanks to his modern understanding of navigation, he becomes the crew's “brains” early on, but never tries to take control away from Luffy.
As he grows, Lin Ye awakens a unique ability: the Echo-Echo Fruit, which lets him briefly copy afterimages of other people's moves. This allows him to combine attacks with Luffy's Gum-Gum Fruit, as well as use imitated moves to cover his companions at critical moments. He witnesses Zoro make his vow, Nami beg through her tears, and Sanji say goodbye. Each time, he stands beside Luffy as his “brother,” sharing the dangers with his own strength, while always leaving Luffy the glory of becoming “the man who will be Pirate King.”
At its heart, this isn't a story about Lin Ye replacing anyone. It's about him experiencing that passion and camaraderie all over again as someone on the inside. He steals meat with Luffy, laughs at Usopp's lies, and, during the Paramount War, breaks down alongside Luffy over Ace's death.
