X 3-in-1 Edition volume 6 collects volumes 16-18 in omnibus format and features story and art by CLAMP.

Subaru and Seishiro face off in a desperate battle on the Rainbow Bridge, as the years of twisted love and bitterness between them lead at last to their inevitable, heart-rending culmination. In the tragic aftermath, with their kekkai failing and their Dreamseer's predictions foiled, the Seven Seals split up and roam Tokyo in an attempt to halt the destruction engulfing the city. But time is running out. The time of the final battle between the Dragons of Heaven and the Dragons of Earth is drawing near...