A massive "Ultra Flare" from the sun envelops the earth, and Spark Dolls are turned into monsters. To deal with the outbreak, mankind forms Xio, a special defense team. 15 years later, Xio battles a monster when a mysterious voice says, "Unite! If you and I join together, you will fight that monster with one heart, one mind!" He agrees, merging with a giant of light to become Ultraman X!
