"The last monsters, created of evil, crawl beneath the dirt of the earth. Finish off the monster army in diggings and dirtings!!" - In game description.
Diggings is a route to Dirtings which holds the task item.
In the northeast corner of the map is a room with a townsperson named Lucy. Next to her is a room full of diamonds. Ha ha.
Angel: there does not appear to be an angel in Diggings.