He had a goatee, thick eyebrows, and a mustache.
He was shown to be a sharp and observant individual.
During the Battle of Sai, Sou was informed by his subordinate that their forces were being pushed back, and it was then that he first saw a flashy looking kid running around the battlements and noticed that due to the kid's appearance the militia suddenly caught a second wind. Sou also noticed that this person had special bodyguards with him and soundly concluded the he must be some Qin VIP.
In the midst of the skirmish, Sou arranges for the bodyguards to be shot by a volley of arrows that initially seemed strays, but that were meant to give him the opening to lash out and take down that kid, who, Sou still didn't realized, was none other than King Ei Sei himself. However, Sou underestimated that boy's abilities, and had his arm removed by a swing of his target's sword.
Wounded but showing great determination, Sou slammed his body into Ei Sei's, grabbing him with his remaining arm so that his man Ban Riku could finish the job. Ei Sei barely managed to block the sword thrust of this second attacker and was wounded in the neck while parrying. It was only when that "boy" went down on his knees and the entire militia of the city blew his cover by screaming in desperation after seeing their monarch's blood being spilt, that Sou realized who the boy actually was, and immediately ordered Ban Riku to behead the king.
That could have been the end of Qin if not by the fact that Ban Riku was prevented from doing his job after being cut in half by Shin of the Hi Shin Unit, who then proceeded to onslaught the remnants of the Zhao in the area. Captain Sou even tried to launch himself at Ei Sei in one desperate attempt to end it all then and there, but was easily stabbed in the neck and killed by the captain of the Hi Shin unit.