Gatekeeper

The Gatekeeper is a giant, two-headed snake Ayakashi that guards the main entrance to Hakuma's spirit world. Only those who obtain its permission are generally allowed to pass unharmed.

Appearance
It is a giant, two-headed snake. Various areas of its body are surrounded by dark, floating rings, particularly the spots just below its heads.

Plot
Mudou leads Masamori Sumimura to the the treasure room inside Shadow Organization Headquarters. On the ceiling is an enormous painting of the Gatekeeper, which Mudou identifies as the entrance to Hakuma's spirit world. Upon entering the painting, however, Masamori encounters the actual Gatekeeper, who refuses to let him pass without permission and attacks. Masamori has no choice but to fight. The fight is briefly interrupted when a flood of Nichinaga Oumi's psychic serpents also come through the doorway.

Trivia

 * Though Tokine Yukimura used a similar hidden entrance into Hakuma, the ceiling she entered was unmarked, which is why she did not encounter the Gatekeeper.