Much the same as humanity, there was a certain amount of the youma population that simply came into existence, born, if that word could be used given they had no real knowledge of how Youma procreation worked... wrong. They would struggle for life from their first breath, pain wracking their bodies, some genetic trouble or other slowly destroying them from the inside out. This small part of the population was dubbed 'Terminals', for indeed, they seldom lived longer than a few miserable decades. The pragmatic course would have been simply to kill off all the dead weight, however, very rarely indeed, a youma or two would manage to shake off its condition somehow, and in that case would always be many times more powerful than any of their simpler brethren, destined for the elite of the elite, just below the Generals themselves, and those youma they specifically favored for whatever reason.
Beryl had decided long ago that they could not afford the chance of losing those possible powerhouses, and had arranged for them to continue on the same rationed amount of life energy as all the others, continuing their agonized existence.
When the seal had broken and missions came up that would almost undoubtedly be suicide, there was always a flood of volunteers from the Terminals, eager to have what they saw as inevitable deaths mean something, rather than simply gasping for breath, spasming wildly, and then laying still as their bodies disintegrated. To die for a greater cause, possibly even being the key linchpin of a successful mission, rather than simply dying.
More than a few of the Youma that the Senshi had destroyed had been Terminals fortunate enough to be selected to accompany Jadeite on a distraction mission. The Queen hadn't been exactly pleased when she'd figured it out, but if she'd objected and refused to allow them to volunteer for those missions, then they would likely have simply commited a mass suicide out of spite, and so she had had little real choice in the matter.
The keywords had been 'Instant, painless death' and 'Extremely likely'. The Terminals, upon hearing them, had become like wanderers in a desert having been offered water by the bucketload. They fell all over themselves, begging to be allowed the honor of following one of the Generals into a battleground where an end to their pain would likely be tossed around like candy.
They wouldn't sacrifice the mission merely to die, of course, but the survivors would very much envy those fortunate enough to fall in battle.