“Silver-Haired Maiden, or whoever you really are! I knew you'd come! I knew how your reputation would suffer if you abandoned these prisoners here. You had no choice but to come.”
—Radmin fighting Micaiah
You've dealt with many a mage like this before, so this should be easy. Take someone like Nolan who can take care of him in one or two blows, or someone who can double him such as a promoted Edward or Zihark. If you want to take advantage of the Trinity of Magic, you can bring Ilyana, promoted again, of course, or Tormod, both with Elwind.
You can also go the easy way and dispatch him in one blow using Nailah.
Radmin: My forces...overpowered. The enemy fights with such passion... Is this another of the "Maiden's" powers?
- Vs. Micaiah
Radmin: Silver-Haired Maiden, or whoever you really are! I knew you'd come! I knew how your reputation would suffer if you abandoned these prisoners here. You had no choice but to come.
Micaiah: How many innocent, defenseless people have you ordered killed...just to lure me here?
Radmin: Look who's passing judgment! Maiden of Miracles, Savior of Daein... You've spun quite a pack of lies to inspire your conquered people. But that ends here, wench! Let's show them how insignificant you really are!
Radmin: I see the "Maiden" has sub-humans eating out of her hand! Well, your skins will look nice on my trophy wall!
Radmin: What is this?! Sub-humans from Gallia? No, they're different somehow...
- Vs Rafiel
Radmin: A Serenes heron? But how? How did the silver-haired wench find you?
Radmin: That wench...her powers...much too dangerous... She mustn't be allowed...to...