Ultraman: Starting Out as the Strongest Reionics

(The protagonist does whatever he wants. You never know what he'll do next.)

(His personality changes gradually as he comes to understand his true nature. He's no saint.)

The Reiblood once ruled the entire universe with an army of monsters. After ruling for tens of thousands of years, its physical body deteriorated and vanished, but its spirit remained. It secretly spread its genes throughout the universe or possessed others in the form of a soul, searching for a new heir and plotting to reclaim its position as ruler of the universe.

Lei Luo, who transmigrated to this world, carried Reiblood factors within him and became a Reionics. He then set off on a journey to become the greatest monster trainer in the universe.