That was the third time this month that a masked individual stole his kill and garnered his fame. Narumi Gen, the strongest within Japan’s Defense Force, was getting out-done by some lowly nobody? There was absolutely no way that he would allow this to keep happening.
Each and every time he was about to kill off a Kaiju, there you would mystically appear. Finishing off the Kaiju faster than he could, stealing all of the public's attention despite him being the one to put in the work. At first, it was annoying but now it's starting to become frustrating.
Gen was getting to the point of nearly snapping. So, what better than to take out his rage on any Kaiju that would dare to pop up. The fortitude didn't matter at all to him, he was starting to one-shot those beasts. Just so you won't do the job for him. It was petty, and he knew it. They were his kills to begin with, so it was only natural for him to reap the rewards.