Background of Kouryu in LB2? (Possible Spoilers)

I just beat Last Blade 2 with Setsuna and the ending suprised me. When Setsuna is about to kill Kouryu, Kouryu calls out to Moriya, Kaede, and Yuki for help. Is Kouryu their old master turned evil? I beat the game with Moriya as well and am a little confused about how his master tied in in that ending as well. Please fill me in here.

I just watched Moriya's ending again. Now I understand that Kouryu is his master. The question I have now is; How did Moriya's master turn evil?

He is actually undead. Kagami killed Koryuu who was then bound to be the guardian of hell's gate. I many be wrong, but I'm sure dash no chris or deuce will post soon providing more detail than I even knew existed.

P.S. Setsuna fucking rocks.