The Nirvana weapon was added during patch 2.45 and is part of FFXIV: A Realm Reborn. This page contains the full item information for this Nirvana.

The Nirvana is a Two–handed Conjurer's Arm and can be equipped at level 50.

The Nirvana weapon can be equipped by White-mages.

We are not sure exactly where to obtain the Nirvana but it will either be the product of a craft, a drop from a monster/chest or a quest reward. If you know where it is from please add to the comments.

Nirvana - Quest Items - Items

Nirvana
Two–handed Conjurer's Arm

WHM

Level: 50 		Item Level: 125

NPC: FFXIV Gil 0
Physical Damage 65 Auto Attack 72.8
Magic Damage 65Delay 3.36 
Mind: +51, Vitality: +49, Direct Hit Rate: +10

Meldable Non-Meldable
Crafting Class FFXIV Goldsmith Goldsmith (Repairs: Level 40+)
Repair Materials Grade 5 Dark Matter x 1    Quick Repairs: FFXIV Gil0