Leviathan

Leviathan serves as the sea deity of the world known as Éclair, sharing a deep bond with the protagonist Yuki (Seitz) that traces back to their previous life as a hero. When Yuki is summoned to the other world for the second time, the two reunite upon the ocean, rekindling their connection. Appearing in the form of a blue-haired girl, she wields tremendous power over the seas and holds profound trust in Yuki, frequently acting as an indispensable source of support during ocean crossings and battles.