The argument is that he apparently won't go to using that unless he's very desperate
Well, he will summon Demonbane pretty quickly. The problem is the Shining Trapezohedron and presumably Athleta Aeternam, though legit as described, are finishers. I'm also not sure what's with the 'size of the universe' thing. There's a lot I can't account for because the sequel VN didn't get translated.
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"As the size of an explosion increases, the number of social situations it is incapable of solving approaches zero." -Vaarsuvius, Order of the Stick