When a young girl named Hisako Ichiki goes missing in northern Japan, her parents seek help in Professor Xavier, who calls on the X-Men to unite.

The X-Men carry out an investigation that leads them to the U-Men, a group of mad scientists whose hideout contains a horrifying secret.

Hisako's mutant powers are weakened during a fierce battle between the X-Men and Todd, the U-Men's mad scientist.

The X-Men are put at risk of secondary mutation when the Blackbird is attacked by a bat-like creature showing dangerous signs of Damon-Hall Syndrome.

Emma allows Professor Xavier to read her mind and reveal her thoughts after Cyclops opposes her membership in the X-Men.

An intense battle ensues when the X-Men are attacked by remnants of the U-Men after being forced to execute an emergency landing in the Blackbird.

Having defeated the U-Men, the X-Men come face to face with Yui Sasaki at her underground base, where she once ran a school for mutant children.

After falling ill with Damon-Hall Syndrome, Riko and Kaga attack the X-men's base, while Emma spies on a stranger in her diamond form.

Revelations abound when it's discovered that Riko and Kaga were drugged by Yui and that Jun and Mastermind are one in the same.

Mastermind's evil plans are frustrated as a fierce battle between the X-Men and the Four Pillars of the Inner Circle rages on.

The X-Men mount an attack to bring down Professor Xavier's son, Takeo, before he destroys the world, putting an end to both mutants and humanity.