The younger sister of the X-Man Colossus, Illyana came to live with her brother after being kidnapped by the eccentric assassin Arcade. Months later, the sorcerer Belasco captured Illyana and held her prisoner in the pocket dimension Otherplace, a.k.a. Limbo. Belasco turned a portion of her soul demonic in nature, and in the process conjured a “bloodstone” gem from her soul. When Belasco conjured five such gems, Illyana, who would have transformed into the entirely demonic Darkchilde, would serve as the means by which Belasco’s demon masters, Chthon and the N'Garai, could conquer Earth.
Belasco’s spell gave Illyana considerable magical power, and she nearly killed him, but decided not to give in to her demonic side and drove him from Otherplace, becoming its new leader. Illyana returned to Earth at a point only seconds after the X-Men’s escape from Otherplace. However, whereas only seconds had passed for the X-Men, Illyana had aged seven years in Otherplace and was now 13 years old. She then joined the team of superhuman mutant trainees the New Mutants as Magik.
Belasco’s former servant S’ym later seized control of Otherplace and spearheaded an invasion of Earth. In an effort to defeat him, Illyana retroactively erased her existence as Magik by using her mutant powers to alter time, and as a result the invasion effectively never took place. Illyana emerged from the enchantment as her younger self, possessing no magical abilities and having a pure soul. Ultimately, Illyana contracted the deadly mutant-killing Legacy Virus and died. It was later revealed that her eldest brother Mikhail had actually given her the Virus after the past New Mutants travelled into the future to meet their present-day counterparts.
Her spirit however contacted both Wolverine and Piotr from the afterlife. She came to Logan shortly after he had the adamantium pulled from his body, and urged him to return to the world of the living to save Jean Grey. Illyana's spirit returned again, this time to her brother Piotr, who had recently returned to the X-Men and the United States with Kitty and Nightcrawler following the disbanding of Excalibur. When investigating odd occurrences inside the Mansion, Piotr located one of stepping disks that Illyana had magically bound to the school. He found himself transported to a pocket world, which held a memory imprint of Illyana. There Piotr manages to learn how to let go a little more and to move on with his life, while still remembering his sister.
Despite this, Illyana's memory convinced him to make one final sacrifice. When the cure for the Legacy Virus turned out to need the death of one mutant, he secretly and willingly gave his life, so nobody else would have to die like Illyana did. Colossus would later be resurrected by an alien race. In addition, when Colossus visited Breakworld it was mentioned by Danger (the Danger Room AI) that the "magic bullet" headed towards Earth held Illyana's genetic signature.