The Demon Sword Master of Excalibur Academy, Vol. 7 (manga)

Leonis and the rest of the eighteenth platoon have returned from the abandoned city, just in time for the Holy Light Festival - a schoolwide celebration jointly held with the Sixth Assault Garden. The dorm's event of choice? A haunted café, complete with tasty treats and cute costumes-including one for the Dark Lord himself! But even during this relaxing moment, evil stirs beneath the surface, and Nefakess has turned his sights to the silver-haired vampire by Leonis's side...