This is why I adore Lunge. He may have his bias'. He has no particular sense of true justice. But he hunts and hunts and hunts. Of course he doesn't take a man at his word about some phantom ultimate monster.
But he can find the monster. He can find the facts. The outline. He is a solitary man, who works terribly with others, relates terribly to others. He is unkind. He is fixated.
But who else, without it being revealed in front of their eyes like it was for Tenma, without being witness to the monsters birth by proxy, could find him?