The Bolontiku are a group of nine Mayan deities, the Nine Lords of the Night who from the Underworld of Xibalba ruled over every ninth night forming a calendrical cycle. They were defeated by Mayan Hero Twins.
The Bolontiku appear deep in Xibalba and are fought before the party reaches the Fuhrer at its heart. Each of them have similar weaknesses to of the party's Ultimate Personas, as well as the dark version of their exclusive skills.
The reason why the Bolontiku are portrayed as aliens in Innocent Sin is due to an extraterrestrial origin interpretation on their myth as the lords of the Mayan underworld, with the entrance to Xibalba being a Dark River visible in the Milky Way, something that could be interpreted as having to cross the Milky Way to reach them. In the game, due to the theories described in the In Lak'ech book becoming reality through the rumors, Xibalba appears as a space ship and the Bolontiku as aliens.