Dungeon no Maou wa Saijaku!?

Synopsis

God left a dungeon in the hands of a boy known as the Demon Lord. After receiving multiple blessings from God, let’s start my life as a Demon Lord! …Or that’s how it was supposed to be, but God messed up and created the worlds' weakest Demon Lord ever. To continue living, I have to continue making dungeons. This story is about an idiotic protagonist, a lonely demons' child, an Undine who lives in a bathtub, and a princess who fell in love with the Demon Lord, even though she was human. A story that all unfolded during a bath.