Sword Labyrinth of the Sacred Sword

Sword Labyrinth of the Sacred Sword summary:

There exists *something* in this world that overcomes human knowledge. That *something*, called the ‘Sword Labyrinth’, is a dungeon residing inside the ‘Holy Sword Gramm’—A humongous relic piercing through the once majestic city of Sigurd. Many adventurers challenged the dungeon, seeking the answer to the mystery behind the never ending beasts born inside the holy sword, only to disappear afterward. The Father of the young Alec, a resident of Sigurd, had also disappeared inside the dungeon. Ten years later, Alec became a ‘Silver Smith’, met the mysterious ‘Sword Queen’ Celestia, and together they ventured into the dungeon… …not knowing that more misfortune than the one his father went through was waiting for him…