The Demon Sword Master of Excalibur Academy, Vol. 9 (manga) — Yu Shimizu

After the mission in Necrozoa, Leo and his friends in the eighteenth platoon return to their everyday lives. But at Excalibur Academy, peace never lasts for long—when an armed group known as the Kenki Gathering appears before Sakuya, the young swordswoman is forced to confront her past. The former royal guards of the Sakura Orchid are consumed by hatred for the Voids, and they reveal a shocking plan…!