Once you have the statue, a "Sword in the Stone" will appear in the maze when you play Swordsman as a main. It will typically appear in one of the very first floors. This doesn't work in Event mazes and might not work in the stage mode runs (to be confirmed).
Click on it multiple times and it will explode like one of Bunny's Easter Eggs. Among the fat loot, you'll find the first time a Dragon Slayer Armor that you can equip (Defense +5) and that gives the fashion "Legendary Swordsman" during settlement.
The "Sword in the Stone" will reappear on later runs and give a nice loot but you'll no longer get the Dragon Slayer Armor.
It seems that the loot often (always?) contains a Sword Skill Scroll, possible scrolls: