The amount of effort Fengo exerted to turn the mages of the Sia Tower into what they are today was not small.
The devils, in fact, have always preferred mages with a high concentration of souls.
But, the biggest factor leading to their failure was also the mages.
After all, the higher the soul power, the more resolute the will.
Even if initially trapped, they might suddenly realize everything at any moment.
Moreover, unlike mortals who hesitate despite knowing they've been deceived, mages, for some inexplicable reasons, would drag devils down with them to perish together.
Of course, before that, they would try every possible means to redeem their souls from the devils… When all else fails, only then would they choose the drastic measure of mutual destruction.
Logically, mages of the Evil Faction aren't very averse to committing evil with the devils, but as soon as they feel their souls no longer belong to themselves, the resistance they unleash is particularly terrifying.
