In the Goshintou series:
Vol.1 - Zettai Meirei
From Psycho Pandas:
c01) Zettai Meirei - Absolute Decree
A wise, genius chief priest, Kikyou, falls in love with the beautiful heroic spirit of a sword, Kazuto. The story of a forbidden love.
c02-05) Rakuin - Stigma
"I have corrupted you...Mikoto." The third sword spirit that cleanses evil, Mikoto, understands what it is to love the gentle fourth sword spirit, Shiou. However, Shiou is used by a political opponent's freed assassin...!?
Vol.2 - Ryaku
Toranosuke has sworn to avenge the death of his older brother, who was eaten by the demon Shunjin. A souleater, Shunjin can only be defeated by one divine sword. But when the time comes for Toranosuke to extract his revenge, can he really do it? Shunjin might be a monster, but there is something about him that draws Toranosuke's gaze. Could the demon slayer be falling for the demon? Can the quest for love triumph over the quest for revenge? [B-U M]
Goshintou