Paradox/Accessories

Accessories are a special item that occupy an armour slot but, unlike armour, they can be used by any character with the only restriction being only one accessory can be used at a time. All accessories can be found in the random red chests of the Labyrinth of Chaos, but those which locations are only tagged there can't be found otherwise.

General
General accessories provide basic modifiers to things like stats or can sometimes replicate abilities.

Books
Books of the western and eastern variety provide boosters to different elements and skill types. 

Pendants
Pendants provide resistances to various damage types and status effects.

Medals
Medals enable weapon and armour usage.

Knowledge
Knowledge accessories enable the holder to use different skill types.

Charms
Charms provide non-combat benefits but may relate to combat like Encounter Rate or amount of Experience gained.

Panties
Panties are an accessory in the same way Monster Milk are a consumable. They don’t actually do anything despite the game classifying them as an accessory, serving as a collectible instead, although you can make characters wear them for no effect. Unlike monster milk, not every character has a pair of panties to collect because some of them don’t wear any.