In the main Marvel universe, Scarlet Witch's actions decimated the mutant population but it was a power loss that resulted in the loss of mutants. In another dimension, M-Day took place years later than in the main Marvel Universe. The Scarlet Witch's powers also had different effect on the mutant population. Instead of simply depowering mutants, her powers unleashed a Legacy Virus. The virus attacked in several stages. The first stage was a gradual weakening of powers. This led to the second stage which was a complete loss of powers. The third stage involved a slow shut down of the body. The mutant slowly weakened until they reached the final stage which was death.

The Legacy Virus was only around for 24 hours before it disappeared. No one knew it at the time but the Legacy Virus was defeated by the sacrifice of two mutants. Jean Grey and Hope Summers combined their powers to channel the Phoenix Force. The Phoenix Force was able to destroy the virus but it came with a cost. Jean Grey and Hope Summers died and the Phoenix Force was weakened to the point where it could no longer possess anyone. The force has not been seen since.

Even though the Legacy Virus was only around for a short time, it had a massive effect on the mutant population. Hundreds of mutants were dead and hundreds were depowered. Those who remained found themselves victim to the rising Purifier movement. The Purifiers came out after M-Day and successfully convinced most of the world that mutants were bad. Whole countries joined the Purifiers hoping to finish the job of exterminating the mutants, a job that Scarlet Witch had accidentally begun.

The mutants that survived were faced with many challenges. They were a minority before the virus but now they were a small number. They also had to worry about the growing threat of Purifiers. The Purifiers were everywhere and they mercilessly exterminated any mutants they could find.

Fortunately for the mutant population, a few weeks after Legacy Day, a mutant boom began. New mutants began to appear everywhere. This caused a lot of the mutants who had gone into hiding to come out to help the new mutants avoid the Purifiers. Heroes and Villains alike tried to recruit as many new mutants as they could especially since of the bizarre side effect of the Legacy Virus. For some reason the virus did cause the mutant population boom but on top of that for some strange reason, most of the new mutants that were appearing were Omega level mutants.

The mutant population in the other dimension has faced many challenges and continues to do so but they are now faced with great opportunity to rebuild. This series tells of how mutants were able to rebuild.