Teogonia

In the harsh region known as the borderlands, humans must fight an endless battle against demi-human creatures that come at them relentlessly, intent on taking their land and their gods. A young boy named Kai, fighting to defend his village, sustains a life-threatening injury that causes him to regain memories from a past life. If you're not a guardian bearer, it's like you're playing life on hard mode… Kai's newfound knowledge gives him a new sense of the unfair "rule set" that governs the world around him. One thing is clear: For those without a god to serve as their guardian, life is a constant struggle for survival. Thus begins the epic tale of a young boy's ascent into a vast world filled with magic, bloodshed, and mystery.

(Source: J-Novel Club)