Centuria, Volume 1 (by Tohru Kuramori)

A selfless sacrifice to an ancient god gives a bitter slave a reason to live and a baby to raise. Sold into slavery by his own mother, Julian has known nothing but pain and brutality. All that changes when, aboard a slave ship, he experiences the kindness and tender touch of a loving person for the first time. But fate has plans for Julian in the bloody awakening of an ancient god who strikes a cruel bargain: an innocent life in exchange for extraordinary powers—abilities he must use to protect a helpless baby in a cruel and violent world! 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!