The World's Least Interesting Master Swordsman: Volume 2 by Rokurou Akashi

Master Suiboku's given Sansui his blessing, so in addition to guarding his mistress, Lady Douve, he's now offering instruction in swordsmanship. Not only is he teaching his fellow Japanese transferee Saiga and the foreign prince Tahlan, but he's somehow found himself teaching the city's ne'er-do-wells and the Royal Guard. Meanwhile, House Caputo, a Great House of the Arcana Kingdom, is fighting a war with the Kingdom's neighboring nation. Evidently, the army invading the Caputo lands is equipped with cheat items, but House Caputo's got a cheat of their own up their sleeve.