Real-life Slime Earrings, by Etsy crafter CoPirate. ”Disclaimer: may not improve defense,” but may improve chances with Kelsey Weaver. Also available in Metal Slime, and as a phone charm (also available in Metal Slime), but those aren’t in-game items, so whatever.
Buy: Dragon Quest IX
See also: Our attempt to corner the market on random Dragon Quest IX content
