Nothing

Here is an aura that does what it says. Nothing is a Basic aura added in Eon 1-5 with a chance of 1 in 1, which is the least rare figure possible, but it can only be rolled in The Limbo. So the difficulty is not the roll, it is getting there: the Sol's RNG Wiki says you must complete the tricky Limbo questline and then enter the area to roll it.

Equipping it changes nothing. No effects appear and the name above the player is missing as well, which the wiki says makes it the third aura without a title after pukeko and Duke. Its text style resembles Nihility's. The in-game description is simply "It's Nothing...".

The wiki records a secret-keeping story. Before Eon 1-5, hschu_hschu said on Discord that it was unobtainable and hinted it would arrive later, 53_Axis showed it above Common in the collection during a stream, and a mini-update in Eon 1-4.5 removed it from the collection so it would remain a secret until the real release. By displayed rarity alone, it is the least rare aura in the game.