I read comics and I actually don't really know much about Nico or Robbie. But if you're after Magik I'd recommend

https://www.amazon.com/X-Men-Magik-Storm-Illyana-1983-1984-ebook/dp/B073PK6ZYR/

Colossus' 7-year-old sister Illyana Rasputin has been snatched away by Belasco, demon lord of Limbo! Though the X-Men rescue her what seems like seconds later, those seconds represent a years-long ordeal for Illyana - one that starts with losing a piece of her soul, and goes downhill fast! The sorceress Ororo and feline warrior Cat - alternate-reality versions of X-Men Storm and Kitty Pryde - aid young Illyana against the terrors of Limbo, including Belasco's henchman S'ym and a twisted, perverse version of Nightcrawler. Trained in good and evil magic, Illyana learns to control Limbo's teleporting Stepping Discs - but as the final battle against Belasco arrives, can good triumph over evil when Illyana doesn't know which one she is anymore?

Illyana isn't just a simple mutant.... she's a mutant sorceress who rules the demonic realm known as Limbo. And this 4 part mini tells the story of how that happened.

I'm 99% sure it was just done as a way to super age Collosus' kid sister because they were bored of her being that age, but the whole "Demon Lord" thing is a bigger part of her character than her mutant powers now.