Being born as a Beorn, made him a resident of Beorn Village located on a distant island from Regno. What irritated Netnu is that the island was led by a human, Dongorio, to which he wanted to put a stop to. Netnu rallied up many of the other Beors and started the Beorn Rebellion, exiling Dongorio to Regno while Netnu himself was crowned as the new Beorn leader. At some point however Netnu aspired to become more and made a deal with the devil, yet he didn't want to lose his soul, but said he would offer many others. The Beorn Village was set in flames and Netnu managed to escape, with some separated limbs, and managed to find his way to Orientis where he joined Eric on his side and got replacement limbs from Colette.
Nentu can be described as being the polar opposite of Unten. The Beorn is an egoistical person who only does what is good for him. When he does something for someone else it is because he will profit from it, always putting himself at an advantage by using people. He is set to achieve his goals in life, which is making the world a good place for Beorns, even using Eric for it. Most people experience him as arrogant and self-centered.
While Netnu doesn't have any special born abilities, he has a mind that always thinks multiple steps further. His steampunk limbs enhance his strength, and also equip him with one of Colette's new experiments, which is to actually have a flamethrower as hand.