The Demon Sword Master of Excalibur Academy, Vol. 3 (manga) — Yu Shimizu

As Leonis continues with his plans to rebuild the Dark Lords' Armies and search for Roselia, he gets wind of the Imperial Princess Altiria's visit to the
Seventh Assault Garden. Seeing it as a good opportunity to learn more about this world's royalty, he seeks an audience with her -- but others have more sinister plots in mind. When Voids attack the princess's battleship and the mysterious Demon Swordsmen emerge from the shadows, Leonis must do all he can to protect his new kingdom without giving away his power...