Centuria, Vol. 1

Caught as a stowaway aboard a slave ship, Julian narrowly escapes death by the kindness of fellow slaves who take pity on him, especially a pregnant slave by the name of Mira. But when the slaver decides to liquidate his holdings, the bloodbath calls forth an ancient god from the sea. A deal is made at the cost of a life and Julian is forever changed, gaining fantastic powers. But even with his new abilities, monsters at sea and on land pose a threat in this dark and dangerous world!

Volume 1 of the Centuria manga series by Tohru Kuramori.