Wer hat Daigoro Tokuyama ermordet?

Two assassins face off at a certain "workplace." The cool bounty hunter Chateau and the mysterious and powerful Ryang-Ha. Chateau and Ryang-Ha become enemies after this fight—at least, they should have, but for some reason Ryang-Ha takes a liking to Chateau and begins following her around. Little by little, Chateau develops a cooperative partnership with Ryang-Ha, which gets her caught up in the struggle against the organizations hunting him down. Furthermore, that battle is related to her past as well. Why did Ryang-Ha approach Chateau? What is Chateau's secret past?