Seafaring: Two Sea Kings in One Family, and My Little Sister Is Shirahoshi

Caesar transmigrates into the world of One Piece and becomes the prince of Fish-Man Island.

His younger sister, Shirahoshi, is Poseidon, one of the Ancient Weapons.

After activating the God-Tier Sign-In System, all he has to do is sign in to obtain abilities from countless worlds.

Sign in at Fish-Man Island and obtain the divine Sea King's Trident and the Poseidon template!

Sign in across the Four Seas and obtain Conqueror's Haki!

After obtaining Poseidon's abilities,

Caesar and Shirahoshi become two Sea Kings in one family.

The siblings set sail and embark on a journey across the world.

Garp: "Shirahoshi's ability to summon Sea Kings is terrifying, but her brother Caesar is even more terrifying!"

Sengoku: "Why can both Caesar and his sister summon Sea Kings? Which one is the true Ancient Weapon?"

The Five Elders: "Even the Ancient Weapon Uranus would be no match for Caesar!"

Imu: "Caesar possesses the power to destroy the world!"

This novel and its characters are entirely fictional. Any resemblance to real people or events is purely coincidental. Do not imitate.