In reality, Archemorus was one of three legendary heroes of Cantha who together bested Shiro. Vizu, an assassin, incapacitated Shiro, causing him to drop his blades. Then, Archemorus and the Kurzick champion Viktor killed Shiro with his own blades.
Warning: The following text contains spoilers relating to the plot of the Factions Campaign.
The Luxons keep the memory of Archemorus alive by holding a gladiatorial competition every Convocation to see which clan will gain the right to bear the Spear of Archemorus to slay Zhu Hanuku, the Kraken.
The Spear of Archemorus plays a vital role in Master Togo's plan to vanquish the returned Shiro Tagachi. When dropped, you will see a male figure rising up out of the spear. This is the spirit of Archemorus. Note that he is wearing the Elite Luxon Armor that is available to warriors at the armor crafter in Leviathan Pits.