He had known since childhood that some people would push others into hell for their own gain. They turned others into monsters for their own benefit, then told the onlookers how terrifying those monsters were. He wanted to drag those people down and trample them into hell. So he had to defend the wall, protect the people fighting alongside him behind it, and protect the person who had made him their whole world.
I like DaDa's books. Can I be friends with DaDa?