Hollow Technique #7: False Endless.
It was more akin to a curse than a blessing, considering how it operated on the victim.
The soul of the False Endless would be in the possession of the Hollow Technique User, while the body would be in a state between life and death.
In essence, while Justin couldn't die, he wasn't particularly alive either.
He was Undead.
His Soul was also in the custody of Ater, and that was the only main weakness he had.
No matter how much damage his body sustained, he wouldn't die as long as his Soul was intact. He would keep recovering, over and over again. He could also perfectly adapt to the damage inflicted on him, which meant no single attack could kill him twice.
Of course, it wasn't like this made him invincible.
A False Endless was far from perfect, and was still subject to a lot of limitations.