He is an Underground companion of [Levi](https://anilist.co/character/45627/Levi), [Furlan Church](https://anilist.co/character/87928/Furlan-Church), and [Isabel Magnolia](https://anilist.co/character/87929/Isabel-Magnolia). He is known to be a calm and considerate person to other people living in the Underground city. Yan is one of the underground companions who gets paid by Furlan Church. Since Furlan knows well that Yan needs more money for his leg treatments, he gives Yan more money than usual.

The young Erwin Smith is a rising star in the Survey Corps, humanity's only hope of defeating the man-eating monsters known as Titans. Ruthless and dispassionate, Erwin's mind is devoted to strategies and intrigue. But beneath Erwin's feet is another world, the Underground, where humans are born and die surrounded by the garbage the Capital throws away. Here, the criminal Levi survives on his wits and agility. But when these two ambitious men cross paths, who will prove himself stronger?
 
(Source: Kodansha USA)
 
Note: Includes the prologue and 2 extra chapters.

This prequel to megahit Attack on Titan answers the questions: How did Captain Levi of the Survey Corps go from street thug to humanity's strongest soldier? And how did Commander Erwin become a cold, calculating leader, ready to sacrifice anything to save the human race? The fires that forged this bond of loyalty and trust were intense indeed!
 
(Source: Anime News Network, revised)