[Nuclear]

Iahsus Shard (150 asagos)
Once per 12 or 24 IRL hours, create a random dungeon at your level. Sacrifice murai to add prefixes (Giant, Crazy, etc.) Alternatively, make them cheap (10 asagos), one-use items with only a 6 hour cooldown.

EDIT:
Note: The murai cost would be relatively high (Increments of 500 murai per prefix? Or possibly set costs for each prefix, depending on how desireable they are.) and no murai would be gained from battles inside this dungeon to avoid essentially a free money generator.