One Piece: Just A Big Brother

Vulcan, the true-born son of the legendary pirate Whitebeard, grows up under the care of Vice Admiral Garp alongside Ace, Sabo, and Luffy. Acting as the responsible, guiding big brother, Vulcan shares in their adventures and bonds deeply with his adopted family. However, his path diverges when Garp takes him to join the Marines, believing it's the best way for Vulcan to protect his brothers and maintain justice.

Armed with the power of the Meiso Meiso no Mi (Meditation Meditation Fruit) and mastery over all three types of Haki, Vulcan trains under Garp and Zephyr, rapidly rising through the Marine ranks. Torn between his role in the Marines and his pirate heritage, Vulcan develops a more nuanced view of justice, punishing criminal pirates but sparing those who seek only adventure and freedom.