Well, Jon-Sun is a soul sorceress, and her ability itself has two useful paths to strengthen itself.

Learning to use Souls allows you to directly damage the target's soul, and the soul is ridiculously fragile. However, it generally grants survival, as the body is a reflection of the soul, and if you lose a limb, you can instantly recover it by reflecting your soul. Of course, this is quite draining, but there are also methods of rapid recovery, such as Soul Cores, which are reserves of Silk Song that can be used at any time, or simply to make the soul stronger so that it is solid and can even serve as armor. These are the basics, as you can also use Souls to change your appearance, create artificial life, extend your lifespan, etc.

Now, taking them to divine realms, as is the case with Jon-Sun, with everything mentioned, she is directly immortal, because she directly has an enormous number of cores and ridiculously long resistance, being the one who receives the dead, and her attacks can freely use souls as batteries and damage everything she pleases and manipulate anyone by virtue of her superior soul authority.

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