"Nihlo, Bethany, Jonathan, and Odessa, you stick with William. Your role is defense and support for this Boss fight." Mikaela ordered. "Everyone else, with me. You'll be offense."
Nihlo and the Irisa siblings were picked out for defense exclusively because of their Elemental Affinities. Nihlo's only Affinity was the Earth Element, but because of this, he had a lot of time to focus on the single type of Magic.
Among the class, Nihlo was confident that his mastery of the Earth Element outperformed everyone else. At least, that was true before he met William.
Bethany Irisa had the Light, Sound, and Plant Affinities, which didn't place her in an offensive role, nor was it very defensive. Her greatest advantage wasn't actually Magic, but he noticed that she was much more perceptive than the rest of her classmates; likely something to do with her eyes.
