Magic Items

Wondrous item, common (requires attunement by a spellcaster)

Etched with eldritch runes, this 1-inch-diameter ruby allows you to use a simple or martial weapon as a spellcasting focus for your spells. For this property to work, you must attach the ruby to the weapon by pressing the ruby against it for at least 10 minutes.
Thereafter, the ruby can't be removed unless you detach it as an action or the weapon is destroyed. Not even an antimagic field causes it to fall off. The ruby does fall off the weapon if your attunement to the ruby ends.

This item is found in Xanathar’s Guide to Everything.

The Undisputed Multiversal Championship belt is made of polished gold and inlaid with decorative gems. The blood-red rubies inset into the belt can be removed only by the reigning Multiversal Champion. Once removed, they function as rubies of the war mage.

Bracers of Defense

Wondrous item, rare (requires attunement)

While wearing these bracers, you gain a +2 bonus to AC if you are wearing no armor and using no shield.

This item is found in the Dungeon Master’s Guide.

These bracers take the form of red satin evening gloves, and are incredibly soft and surprisingly warm. Featuring detailed golden embroidery depicting the brutal slaughter of duergar rebels, these gloves grow warmer when within 100 feet of any elemental.