I Kept Pressing the 100-Million-Year Button and Came Out on Top, Vol. 10 (light novel) — Syuichi Tsukishima

a battle between dark and light shadows…Returning from a visit home, Allen is invited to the mansion of Patriot Bolnard, head of one of the most influential houses in the noble faction, who urges him to sit out the upcoming war. Meanwhile, back at Thousand Blade, it's the start of the new school year! Thanks to drastic changes made to the academic schedule, Allen and his friends are immediately thrown into the Sword Master Festival, where they face the strongest of the Elite Five Academies, Divine Emperor, in the very first round. There, Allen finds himself up against Holy Blade Shin Rex and his logic-defying Soul Attire, who pushes him to the brink of death…and beyond!