Sten is one of the Four Rakshasa Temple Demons who serve as the Prime Minister's squad of executioners. He seems to think of murdering as "releasing one's soul."

Sten is a large man with a heavily muscled build similar to Ibara. He has a long braided hairstyle with hair sticking far out at the sides and bald at the top of his head. He has long bushy beard and mustache, bushy eyebrows, and dark prominent circles around his eyes. Similar to his fellow Rakshasa Demons, he wears armor plating on his forearms. He also wears a large Iron pauldron on his left shoulder.

In Chapter 36, Lubbock hits him with a spear made of threads. Sten is able to withstand the attack, but Lubbock uses the threads that pierced Sten's body to cut his heart into pieces.
(Source: Akame ga Kill Wikia)