Nebula Fragment

Nebula Fragment is a Hardmode end-game material. It is dropped from the Nebula Pillar during the Lunar Event. The Nebula Pillar drops 12-60 fragments on normal mode, and 18-90 on Expert Mode. Crafting all of the Nebula gear requires 127 Nebula Fragments and 68 Luminite Bars (272 Luminite). It is used to make end-game magic-related items, including the Nebula Armor.

Trivia
Nebula Fragments are similar to the souls of the anime Soul Eater

Fragment Nébuleux 성운의 파편