The Invincible Shovel (Light Novel) Vol. 3 by Yasohachi Tsuchise
Alan is the strongest miner in the world, able to reduce mountains to rubble with simply a swing of his trusty shovel. But when Princess Letitia begs him to escort her on a quest to save her kingdom from an invading demon force, he agrees to leave his solitary mountain abode and venture forth, on one condition: she must help him find a successor to train. In this hilarious fantasy tale for fans of RPGs, evil doesn't stand a chance against the mighty power of the shovel!