I Want to Be a Receptionist in This Magical World, Vol. 8 (Manga) -

Nunnally and Rockmann's duel is cut short when the barrier protecting the arena is overwhelmed by a sinister, destructive force. Everyone in attendance at Walhelnus is now focused on a single point. When the smoke clears, before them stands the demon of legend, Städal, who plunges the stadium into chaos. If the years have taught Nunnally and Rockmann anything, it's that they stand the best chance at victory by each other's side--vexing as it may be. But in the face of an ancient and terrifying evil, will the combined powers of fire and ice be enough to prevent them all from being swallowed up by the darkness...?