Zieg is a NPC that handles most of the major weapon exchange upgrades. Lore wise, he is a weapon craftsman and has a workshop on one of the ARKS Ships. His shop menu is divided into four menu options.
Introduced in Episode 4, this menu option has the majority of the weapon exchange upgrades. From here is where one can upgrade a weapon series such as the Atlas series of weapons or the infamous Lightstream series, provided they meet the material exchange cost.
If the weapon series permits it, one can exchange the weapon for another type of weapon of the same series, upon a material exchange cost.
This menu option allows for one to exchange certain stone and crests for powerful weapons. The Profound Xion and Invade-NT weapon series can be obtained from here. They are crucial components for the Lightstream series and Austere-NT weapon series respectively. By exchanging certain crests, one can also obtain powerful weapons.
The original exchange menu from Zieg, introduced in Episode 3. Allows one to exchange and obtain Lambda Grinders, Genesis/Embodied Camos, Old Type Invade series, Old Type Austere series, Orbit series, & the Fahren series.