The Demon Sword Master of Excalibur Academy, Vol. 4 (light novel)

AN OLD FRIEND RETURNS With a holiday called the Holy Light Festival fast approaching, the girls of the eighteenth platoon decide to host a haunted café in their dorm. The event is meant to celebrate the arrival of the Sixth Assault Garden, home to Elfiné’s older sister, Clauvia.
The mischievous woman is part of a research team that recently made an incredible discovery in the northern tundra—a massive creature sealed in impervious ice. Much to his astonishment, Leonis recognizes the winged beast as an old rival he never managed to beat. When the monster is set loose to wreak havoc, will Leonis manage to take it down in time?