Kashii is a giant from the island of Elbaph and a loyal member of the New Giant Warrior Pirates. His most prominent early role was as one of the two colossal gatekeepers for the judicial island of Enies Lobby, a post he held for over fifty years alongside his fellow giant and partner, Oimo. Kashii is a towering figure, even by the standards of his race, with black hair that reaches his neck and black eyes, and he typically wears traditional viking-inspired battle attire.

Kashii's personality is defined by deep-seated loyalty and a strong sense of honor, though he can be somewhat naive when it comes to trusting authority figures. Before the events of the Enies Lobby arc, he and Oimo were captured by the Marines while searching for their long-absent captains, Dorry and Brogy. The World Government deceived them, claiming their captains were prisoners who would be released only if the two giants guarded the government's gates for one hundred years. Motivated by this fabricated promise and their profound respect for their leaders, Kashii and Oimo faithfully served for half a century, believing their sacrifice would ensure the safety of Dorry and Brogy.

His role in the story pivots dramatically when the Straw Hat Pirates attack Enies Lobby to rescue their crewmate, Nico Robin. Upon learning the truth from Usopp that Dorry and Brogy had never been captured and were still alive and dueling on Little Garden, Kashii's long-suppressed anger erupted. Realizing the extent of the government's manipulation, he immediately rebelled against his former masters. This act of defiance makes Kashii and Oimo crucial allies to the Straw Hats during the subsequent battle, directly assisting them by carrying members of the crew and their allies to safety. One of his most notable relationships is with his partner Oimo; they are virtually inseparable, having shared over a century of experiences as fellow crew members and gatekeepers. He also shows remarkable gratitude toward Usopp, whom he affectionately knows as Sogeking, for revealing the truth, and even invites the sniper to visit Elbaph someday.

In terms of abilities, Kashii possesses the immense physical strength typical of his giant lineage. He is a born fighter, and his natural power is so great that ordinary humans have virtually no chance of defeating him in a contest of strength. In combat, he wields a large metal axe and carries two shields, demonstrating proficiency in both offense and defense. His stamina and physical resilience are extraordinary, allowing him to endure long-term labor and survive significant injuries. More recently, Kashii has appeared as an active member of the Giant Warrior Pirates in the Elbaph arc. He is found in a wounded state within the Sun World realm, urgently pleading for help as he informs his allies that the elder Jarul is in grave danger, showing that his sense of duty and loyalty to his comrades remains his primary driving force.