This article's content is accurate to the most recent public game version, 0.4.8d.
"Magical nectar mixed by fairies that recovers KO'd allies."
Fairy's Nectar is a consumable item that recovers a knocked out ally, restoring them to full HP.
This is currently one of only two items (the other being the far more common Fairy's Dust) in the game that allow for recovering a knocked out ally. Unlike Fairy's Dust or the couple of skills capable of recovering knocked out party members, Fairy's Nectar is capable of instantly restoring a knocked out party member to full health making it extremely powerful. To go with this strength however, it is also an extremely rare item with only a handful available in the game from chests. Use them sparingly in important situations.