This old book contains an illustration of a monk performing a ritual on a fallen enemy after a fight. Next to the artistic illustration is a mantra. 

“After all sentient beings are saved, will I attain Buddhahood, before the hell is empty, I will not become Buddha„

This mantra contains the law of salvation, it's a technique used for purifying souls it could also promote karmic virtue. Ki power is payment for bringing peace and freeing souls from the earthly world, like a source of karma or virtue. The ferrying mantra could be like a ritual, with a duration of 1 minute per enemy.

• The target can’t become undead by any means, because his soul is no longer part of this world.
• Each enemy ferried makes recover ki points equal to 1d4 + bonus of proficiency.
• Every time you perform the ritual you have +2 damage on all undead for the next 8 hours.