In this world, most humans pursue the path of Reinforcement Wizards, seeking to strengthen themselves by acquiring the bloodlines of powerful creatures. Strictly speaking, Reinforcement Wizards also fall under the category of Bloodline Wizards; it's just that most humans are not born with bloodlines and have to acquire them through external means to incorporate into their being.
The Thirteenth Legion's garrison island has a huge fortress, inside which is an inter-world portal. It is said that this portal was built by the Sea King Empire's first Emperor, who was also the most powerful one. It can connect with other worlds by consuming a massive amount of resources, thereby establishing a passage between two worlds.
There are a total of twenty-one such portals. Eighteen are controlled by different Sea Kings, and the remaining three are in the hands of the Sea Emperor. The one guarded by the Thirteenth Legion is just one of these.
