Siss is a member of the Scouting Legion who participates in the 57th expedition.

Siss first appears as a member of the expedition mounted from the Karanese District into the Titan-infested lands outside Wall Rose. He works with Ness to take down a deviant Titan in a field where their 3DMG can't be used to full effect; Ness takes out the Titan's ankles, and Siss destroys the nape of its neck when it falls.

Note: Siss is the official English translation by Kodansha.