The royal family of Martendale are said to be of divine lineage, and at dire need, the reigning monarch can sacrifice themselves by allowing a charging unicorn to pierce their heart. This particular method of death (briefly) substantiates a portal to the domain of their godly ancestor; however, the ritual has now been modified to allow the people of Martendale to retreat into the Astral. Unfortunately, the quick succession of monarchs may soon run out, and there are many corners of Martendale that have yet to be evacuated... Luckily the unicorns blessed the Martendale House with fertility and high birth rate.
It's also said that some of the aristocratic families managed to abduct members of cadet branches of the royal family who became nobles in neighbouring kingdoms, likely for 'use as conduits' into pocket realms or other planes....
Enacting the ritual in the astral plains allow the unicorns to absorb the noble' soul for safe-keeping; there may be more ways than one for getting it out again... These joined souls unicorns are considered holy.
The unicorns allied with the Martendales have their own noble blood lineages. Each unicorn is bound to a Martendale and are considered like a family member by the House. Mourning unicorns who pierced the heart of their bound nobles are highly respected by other unicorns.
Their is rumors of a Martendale necromancer who use a dark unicorn to pierce the reanimated hearts of her family members.