@Lightbrand From what I'm reading from this chapter and the next, Magic Kings are a natural law of the universe, a tool used to destroy parallel worlds as part of a cycle of rebirth. The father of Lilith, because of his theme based on Lust, did not feel satisfied just being a cog in the machine and sought to carve his own path. However he is apparently powerless to change his own destiny in his own world, probably because he was almost done destroying his own world anyway. So he sent his daughter to "this world" as a linchpin between the two, otherwise non-intersecting worlds. That way, when the Sky Library summons their ultimate anti-Magic King weapon--a fragment of a real Magic King from another world--he would be the one who would most likely be chosen. (I think the Sky Library or an equivalent also exists in his own world too, which is why he thought the plan would work.) Once he was summoned, he decided to wait for Lilith, the key to restoring his powers, to come to him. As the linchpin between two worlds (since she's an existence that shouldn't technically exist), Lilith also seems to act as a node between Arata's world and the remains of his own world where the rest of the power is stored (since he was only summoned as a fragment, like a severed head of a whole body). I'm not sure why he decided to lay around instead of searching for her. But knowing both his and Arata's personality (since all true Magic Kings always seem to be some version of Arata) he likely found it to be too much of a pain to look for Lilith, and he whimsically decided to leave everything to fate or foresaw their reunion as an inevitability. Once he regains his powers that cost him his world, as an outsider to "this world," he can move freely like a rogue chess piece, to destroy everything and rebuild everything according to his own will.
Tl;dr The guy has a lust for even greater power, is tired of being a pawn of the universe, executes a convoluted plan to become a second true Magic King in a world where there should only be one, then tries to become its god