"You’re past your prime, old man." With that remark, the swordsman Kenneth is abruptly expelled from his S-rank adventurer party.

What they are unaware of is that Kenneth’s real identity is the legendary "Ultimate Idle Master," known to only a few. For him, adventuring with a party was merely a pastime to alleviate his boredom.

In pursuit of a new method to entertain himself, Kenneth aims for the unexplored Labyrinth of the Gods, a dungeon reputed to be insurmountable for mortals. During his journey, he allies with Lily, a gunslinger, and Karen, a talented mage. Utilizing his extraordinary swordsmanship, Kenneth begins to dominate the labyrinth, even overpowering the gods that govern it…!!

This marks the beginning of an extraordinary heroic saga featuring a remarkably powerful yet constantly bored middle-aged swordsman alongside the enchanting girls who accompany him!