Griffith, a warlord from the ancient world, leads a group of mercenaries called "The band of the Hawk". They have achieved many victories and ultimately desire to build a kingdom of their own. Griffith has come across an ancient artifact called the behelit, a magical cauldron that can imbue those placed into it's chemical liquid with enhanced abilities. This process doesn't work on adults, as they are fully grown and developed, and will likely kill them. Therefore, Griffith determined to increase the number of soldiers under his command by kidnapping children from conquered territories and using them for the behelit transformation.
The band began experimenting with different ages, cutting babies from their mothers wombs and working their way up to young children. They finally settled around the Goldilocks zone of children in their puberty stage between 10 - 16 years, as this is the range with the most success. Candidates are dumped into the liquid and changed into fully grown demonic soldiers called Daka within a few months. Although horribly disfigured and possessing low intelligence, the soldiers have enchanced physical strength, speed, and durability, making them far superior to normal men. They have become the perfect grunts for the band, completely obiedient to their master's and difficult to kill.
The problem began to be noticed later, as the soldiers life expectancy has decreased. Although incredibly tough, their bodies begin to break down after about a year, finally giving out within three years. This is through no discernable reason, as they recover from damage almost instantaneously and remain capable of continuous fighting. How can this be the case?