After completing The Sacred Katana, you must change areas (logging out does not count as zoning) before you can initiate this quest.
Head to Norg and as a Samurai, talk to Jaucribaix (K-8) who will mention that a sacred ritual to guide the lost spirits of the dead is needed, but that he's missing a feather from a special bird, found only in the Labyrinth of Onzozo.
If the ritual is initiated while under the effect of Sneak, the monsters will not attack and thus, can be picked off one by one. Note that when they spawn, everyone close enough need to have Sneak on, not just the one initiating the ritual.
Sneak will wear off when attacking a target, so be sure to be far enough from them before using a ranged or magical attack.
Using this method, you only need to fight one of them as long as you give the other one 3 minutes to de-spawn, before finishing off the one you chose to fight.
If you get the message "What do you think you are doing?!" just wait a bit.
If multiple characters are in your party, it is possible for all of them to obtain the Faded Yomotsu Hirasaka after this battle, regardless of which one uses the Yomotsu Hirasaka on the ??? to begin the fight.
If you change areas and don't examine the ???, you will need to repeat the fight.
Travel back to Norg and talk to Jaucribaix to complete the quest and obtain your reward.
Gilgamesh (Captain's Quarters, Norg)
Twenty years ago, a small nation was destroyed by the flames of war, and many died without reason. Your assistance is required in holding a ritual to send these troubled souls to their proper resting place in the afterlife.
SPOILER WARNING: Click here for additional details about this story line.