That's for the god emperor immortality. The Family Head and Zahard have immortality granted by the Administrators and the contract ensure they're immortal, this is a perfected form of immortality within the setting even compared to the others as it's akin to a literal LAW of reality, while ironically enough in VS Debates it wouldn't be as good since we assume that it wouldn't work against other settings.
While Zahard has another contract that makes so no tower born can harm him (King's Contract).
Other immortalities are done via spells and a medium,
Soul Immortality (Floor of Death):
The inhabitants got their souls removed and put into the Spirit Room by two high rankers with help of the Family Leader Po Bidau Gustang, and they now can regenerate from even vaporization in case they were to die, the limit is that they can only exist within the Floor of Death Administrator corpse but as long as their soul exist they will live.
Twenty Fifth Baam used Shinwonryu to kill one of those beings, severing the effects of the immortality from one of the individuals affected by the spell to perma-kill them without needing to affect the beings soul in the Spirit Room in any way or destroying the spell on itself.
New Fourth Corps immortality:
They're a experimental group of beings of the Zahard Empire Army, each born to be slightly outside the laws of the Tower. They are several individual whose individuality are tied to one single being, but since being outside the rules of the Tower is not allowed by the Tower, they have an expiry time they can exist on the Tower as then their being rots away at spirit and body. To avoid that they casted an immortality spell on the main individual which allows him to resurrect the others by assimilating them and then releasing them as individuals again. Resurrecting them in case they get killed or in case that their expiry date (when their sould and body completely rot) finally occurs, it's interesting to mention that White Soul-eating spell to eat the souls of who he killed doesn't stop the man from assimilating them and resurrecting them.
Baam severed the connection of the spell from one of the beings (Aria) whose individuality was linked to the man, simultaneously making her lose that immortality and that individuality link with the man, he doesn't destroy the immortality spell from the man on the others but severs the affected (Aria) from the spell itself; he attributes this ability to destroy spells to Shinwonryu
Armor users/Dimensional immortality:
Armor users have hidden their hearts and main bodies within a pocket dimension completely cut off from the outside which is created by the spell put on the 'armor'. This armor acts as their body in the outside and will reconstruct from any given damage as long as they live, making them immortal due to being hidden in this space.
Imaginary Pocket Dimension Immortality
Karaka is immortal because his true body, his heart, is hidden within an imaginary magical pocket dimension made by a spell in his armor.
In that sense, his "original body"/Karaka's heart is always alive and hidden within this dimension.
SIU Blogpost: Vol.2 Ch.322: 44F - The Last Station (7) said:
This chapter, Karaka's secret is revealed
Because Karaka's heart cannot be found by most rankers,
you can look at it as a form of immortality.
How karaka came to wear a spell-clad armor might be revealed later
FUG's slayers are special and clearly differentiate themselves from normal high rankers.
Regeneration
An extent from his spell is that his body is able to self regenerate.
- Karaka is able to regenerate his body from most of it being destroyed by a powerful attack.
Shinwonryu is a pretty practical anti-hax technique, everything a shinwonryu touches is neutralized and dissipates, just good 'ol molecular corrosive substances like poison? Yeah. Energy attacks and special properties? Yeah. Elemental intangibility? Yeah. Spellcraft? Yeah.
Toryus said:
Like I mentioned, Time stop itself has not been shown in Tower of God so far. What they could do is send Dumas to kill the character due to being a perfect combination of austerity, serious, loyal, immortal and powerful enough. Plus teleporting regenerating spears that can oneshot Top 100 rankers and pierce through their skin as if they were made of butter is kind of... bullsh*t to say the least.
foolisharchon said:
his body inside the armor´s pocket space is as strong if not stronger than his armor
Apparently his body outside is stronger according to Baam, he says that they still haven't seen the depths of Dumas power.
Anyways, worst came to the case for immortals, any of the Family Heads could simply seal them in a sealing circle hide within a floating fortress thousand of kilometers in the air on one of their fortress protected by enchanted defensive walls (Ten Great Families defensive wall fortress are usually enchanted with a mysterious spell that make it impossible to break with physical force or shinsu/energy, only Zahard and 10 FHs have the power to break it)