Furuutsubo (古空穂), or old quiver, are spirits who have inhabited the quivers of warriors who suffered tragic deaths. Sometimes other weapons of the fallen warrior (even their armour) could take on a life of its own using residual life force from their owner. One such example of this occurrence is a man named Miura Yoshiaki. He was a skilled military commander who fought in the Genpei War (1180 -1185 CE).
The Genpei War was fought between the Taira and Minamoto clans in a bid for the imperial throne. Yoshiaki fought on the side of Minamoto and his castle was attacked during one of the worst sieges of the war He bought time for the members of his household to escape, facing the invading army on his own. He was killed as the last of the survivors escaped. After his death, his quiver was so heartbroken at the loss that it became a furuutsubo.
As for the rest of the war, Tomomori, leader of the Taira clan, and throne hopeful Antoku committed suicide at the Battle of Dannoura, thus marking an end to the conflict. Yoritomo of clan Minamoto was quick to establish himself as shogun and crafted the Kamakura Shogunate. This empire would throw Japan under military rule for the next seven centuries.