|Netnu, the complete opposite of Unten.|
Netnu is a malevolent Beorn. He is widely considered the complete opposite of Unten, even to the point of having his name changed to a backwards version of him. His debut appearence was in Team Fanon, and he has appeared in several games since.
Out of any given character in That One Series With a Long and Uninteresting Name That I Do Not Wish to Remember series, he is likely second to Unten in terms of how many backstories and alternate looks he's gained over the years.
After the supposed ultimate destruction of the Beorns, it was revealed that several Beorns escaped their fate via spaceship (as evidenced in Fantendo - Dark of Zeon). Netnu, previously named Kaio, was among these select Beorns, although Netnu wasn't initially selected to go on the ship, thus he stowed away in a small lower part of the ship that was empty as it was about to take off. However, this part of the ship was empty because any living thing in that compartment had the possibility of being negatively affected by gamma rays in deep parts of space, unbeknowest to Netnu. And since the main sector of the ship was protected by a special inner-layer material that blocked out gamma rays and Netnu's compartment wasn't, Netnu was essentially doomed. When the gamma rays finally did hit him, a number of things happened. One was that he became partially blind in his right eye (which explains his recent donning of a monacle). Another was that his once-relatively-calm personality was altered, and he gradually became more vengeful, angrier, and far more agressive and obsessive, eventually to the point of turning completely evil. The final event that happened was that Netnu developed strange fire-like powers, the imminent darkness inside him growing due to the gamma rays. Eventually, Netnu escaped the ship, mad with rage at the universe for constantly bringing him misfortune, and he set back out to Zeon to attempt to destroy the planet himself.
Fissure and Post-Fissure (Original)
Though Netnu is not shown during the events of Fissure, it is presumed that he was flying through the vastness of space, able to survive from the high concentrations of gamma rays throughout space making him stronger, and was trying to find Zeon. Presumably after the events of Fissure, Netnu landed on an unknown planet, donned his trademark monacle, and began to train in order to become stronger and find the perfect foe to which he is matched. Eventually, presumably between the events of Fissure and Underground, Netnu finally reached Zeon in his quest to find the perfect foe and found Unten. After a fierce battle with Unten in which Unten was the victor, Netnu, mad with vengeance and jealousy, immediately developed a seemingly-eternal grudge against Unten, renaming himself Netnu and vowing revenge. Since then, Netnu and Unten have fought many a time, and Netnu has never won.
Fantendo Smash Bros. Shattered
Netnu appears as a starting character in Shattered. Attacking with his robotic arm attachments (one of them being similar to the claws he had in Underground (2014), another replaced with a flamethrower), Netnu is overall stronger than Unten and a lot more dangerous. However, he lacks a good grip, so he can actually slip off ledges if on there for more than five seconds.
His role in the story so far has been just limited to singing "Run Boy Run" during the chapter with the same name, giving Unten confidence to continue forward. It's unknown why he did this right now.
Netnu is cocky and egotistical, to the point where he devoted his identity to being the opposite of Unten after being defeated by him. Although he is arrogant and self centered, he never looses sight of what's important and cares for his wife Ezra. In Fantendo Ultimate Alliance, it is revealed he does little dances when he charges up his attacks.
Netnu has many powers, including levitating and creating things from pure air. He also has the power to bend, shoot and create large amounts of fire and sometimes even other elements (such as ice in the Final Battle). He also has immense strength, the abilities to teleport and strong psycic powers. All of these were caused by Gamma Radiation.
Netnu was severely nerfed in comparison in the reboot. Like Unten's lightning powers, Netnu can spew fire from his palms from Blumps, but these are so limited in comparison that a flamethrower is actually more beneficial. During Underground, he was given technological implants by Grime Corp such as mechanized claws and night vision in order to "hunt" Unten.