Two years into One Piece, Lu Fei had developed the fourth gear. In One Piece's storyline, Luffy finally succeeded in developing the fourth gear after two years of training. This new skill greatly increased Lu Fei's strength and speed, allowing him to easily defeat powerful enemies. The process of Luffy developing the fourth gear was very difficult. He spent a lot of time and energy on training. Luffy had finally succeeded in achieving this level of skill by continuously improving his strength and skills. This skill not only made Luffy more powerful, but it also made him more agile and confident in battle.