81Shiki first appears in Stage 4-9 Central Passage of Megalopolis. Eleven of them are station around the area. It is unwise to fight them due to earning very little experience and zero mag and money. It is recommended to fight four of them, as they stand guard on top of chests.
They appear again in the final mission Army CT-Room of the Neutral route, with a number of them positioned around Snake demons to protect the dragon demons in their blindspots.