One Piece 3D2Y: Ace no Shi wo Koete! Luffy Nakama to no Chikai

After the war at Marineford and the death of Ace, Luffy withdraws to the dangerous island of Rusukaina to train under Silvers Rayleigh. For two years he must strengthen both his body and his command of Haki before reuniting with the Straw Hat crew, but grief still follows him even as his skills grow.

His training is interrupted when the escaped pirate Byrnndi World targets Boa Hancock and kidnaps her sisters, Sandersonia and Marigold. Luffy joins Hancock in the rescue, forcing him to put his unfinished Haki to the test against a veteran enemy while confronting the loss that has shaped his determination to become strong enough to protect his friends.