Dark Fragment

Can be obtained through random drop from Smiling Gift Bag or (the probability is not 100% but very close) by defeating any of the Celestial Pillars.

Material in:

Broken Space

Dark Star

Delta Rune

Void Pocket

Void in a Pouch

Void Runner

Boundary

Broken Time

Data Miner

Fury

Stable Core

'Nightmare in a Bottle'

Dark Orb

Void in a Bottle

Void Core

Voidal Fishing Rod

???

Void Katana