I Kept Pressing the 100-Million-Year Button and Came Out on Top, Vol. 4 (light novel)

After managing to rescue Lia from the Black Organization, Allen is selected to
represent Thousand Blade Academy in the Royal Sword Festival. As our hero uses his
newfound power to score victory after victory against competitors from rival schools,
however, a sinister conspiracy begins to unfold. Meanwhile, Allen and his friends finally
get a moment to catch their breath when their school’s cultural festival comes
around...only for his longtime rival Dodriel and a powerful new foe to launch a surprise
attack on the event!