Greeza is a monster born from the distortions of space, being the manifestation of a "hole" in space that gives off no signs of life. It is the main antagonist of Ultraman X and the final enemy of the series as well.

At some unknown point of time, Greeza briefly met with Ultraman Tregear during his fall into darkness, the latter finding their common ground for their relation to "nothingness". Ultraman Taiga Novel: Tregear's Story／Blue Shadow Fifteen years ago, after it destroyed three planets filled with life, Greeza desired to destroy the solar system. As it raced into the Milky Way, it met resistance in the form of Ultraman X. All for One Both Ultra and the figure clashed each others in their travel sphere forms until they reached the sun, where X takes this opportunity to throw the villain into it. However, this had become his greatest undoing, as the villain's demise had set forth the Ultra Flare, with said wave trapped X in a form of computer data and banished him to the Earth.