Kairō Seal

When Kūkan first obtained Eight-Tails Chakra Mode, his previous seal's outward appearance had changed into four thick lines on his stomach and two seals resembling a circle with small "tomoe"'s appeared on his legs.

By using the seal's key, he can form a gigantic Kairō which would trap Gyūki's body, additionally Gyūki is bounded by chains inside this Kairō. Kūkan used this technique to imprison Gyūki and isolate it of it's chakra.