Siss had chin-length, straight dark hair tied back in a ponytail. He wore the typical Survey Corps uniform.
During the 57th Expedition Outside the Walls, Siss works with Ness to take down an abnormal Titan, with Ness taking out the Titan's ankles, and Siss destroying its nape. Almost immediately after, another Titan appears. Following Ness's lead again, Siss tries to strike at the Titan, but it intercepts and crushes him effortlessly.
- He shares a birthday with Zofia.