Qasai is a kavkem concept of mercy-killing or suicide, integral to their culture.
It's generally true that kavkema fear death less than they fear extended suffering. There is still a trade-off even for the general case - they are willing to put up with some suffering, as long as it is known to be temporary, but they are much more willing to put an end to their lives than a human in a comparable situation would be.
Qasai is more than just a preference of death over suffering. Qasai includes the explicit intention to relieve suffering, be it directly or indirectly (e.g. latter might include a self-sacrifice to get someone else out of danger).
kavkema are taught how to fairly quickly kill themselves at an early age and almost all wild kavkema carry a blade with them to do so - to strike into their jugular and tear the blade upwards to the jaw, in a single, decisive motion. This gesture is practised with shallow thorns so the motion is less at risk of getting botched when it is needed (and to prevent the associated sensation coming as a complete shock).
Killing others is either done in the same way or with a snapped spine - this is practised on prey animals.
Qasai is effectively considered sacred, but it is also not a cure-all, and it is not to be used lightly. A kavkem suffering from their equivalent of a cold virus is not eligible to be killed this way - it's obviously a temporary affliction and it does not sufficiently endanger others. Opinions begin to start to differ once Serrata is considered.
Capture by the Nayabaru is almost unequivocally considered a cause for qasai - mothers whose offspring are at risk will always destroy eggs and kill subsapient hatchlings (although neither of those are formally qasai, as the recipients are subsapient, but the underlying notion is similar) and all kavkema will consider, should escape not be an option, killing themselves or others of their group that may have been incapacitated.
Rapid-acting sedatives interfere with this process, of course.
kavkema that have been captured will routinely seek out opportunities to find death. Much of the struggling that kavkema do in captivity is to increase risk of fatal injury, although this squirming does not always work out in their favour, and they may simply end up with a regular injury - and thus a source of pain - instead.
Ryrhakenema are more reluctant to kill themselves than other kavkema are, due to their responsibility as keepers of stories. They may 'prefer' even several years of capture to death and may take a long time (often longer than they have to decide) to decide whether the chance of rescue is too slim to stay alive.
In addition to such philosophical concerns, it turns out that even kavkema have a survival instinct, and not all kavkema have the mental fortitude (regardless how much they may have trained for it) to kill themselves. A kavkem that has decided that in theory, qasai would be the right answer, has about a fifty percent chance of actually seeing it through.