Segment File

The Segment File is a feature of all 3 Xenosaga games. It involves a series of locked doors located across the world that require a specific decoder to be found to unlock.

Episode I
While on the Woglinde, Shion runs into a soldier named Sergeant Swaine. Swaine explains that there is a bug involving a nanomachine core used for building and construction which is responsible for the creation of a variety of sealed doors across the world. He provides Shion with the Segment File which can be used to track them. Swaine is later killed during the gnosis attack and provides her one of the decoders that can be used to open one of the doors.

Episode II
Shion receives the Segment File from Angelina Swaine, the sister of Sgt. Swaine in Second Miltia.

Episode III
Shion receives the Segment File from Theodore on Fifth Jerusalem near the Mobius Hotel after destroying some crates for him. If the player successfully opens all 15 Segment Address doors, they will receive the item KOS-MOS's Swimsuit.