Xibalba

Xibalba (シバルバ) was the main antagonist of  of Kamen Rider Ghost: Legendary! Riders' Souls!, and a major antagonist in Kamen Rider Heisei. He is a Gamma Ultima of the Gamma who refers to himself as the "Spirit Commander".

In Ghost
Xibalba first appears when he emerges in the human world at night through a portal resembling a Gamma Hole. Drive Chapter He proceeds to stand on the sidelines as Kamen Riders Ghost and Specter gather the Kamen Rider Eyecons by defeating past monsters summoned by Frey.

Xibalba ultimately makes his appearance before the twins and the two Kamen Riders after Specter's unlocking of the OOO Eyecon leaves only one more to go, appearing before the twins and the two Kamen Riders. Swiftly beating back Ghost and Specter as it is revealed that the twins were working together to have the Kamen Riders gather the Kamen Rider Eyecons in order to defeat him, Xibalba proceeds to absorb both Frey and Freya, an act which grants him an even stronger form.

In Heisei
Xibalba was a servant to the Ganma royal family, and was trusted enough by them to have reicieved an Ultima Eyecon. However, he was kicked out after it was discovered that he had plans to one day overthrow them. Angry and resentful of those he had previously swore loyalty to, but still wishing to take part in the Demia Project he had heard tell about, he gathered a small group of Ganma, among them Nara, Mokana and Agape, and brought them with him into the human world.