Before the arrival of a particular useless goddess and extraordinary NEET, Megumin, known as the 'Greatest Genius of the Crimson Magic Clan,' is diligently honing her skills. Motivated by a pivotal childhood encounter, she relentlessly pursues the ultimate offensive spell, Explosion, except when she's challenging her self-proclaimed rival for food. Meanwhile, in Megumin's absence, her younger sister Komekko stumbles upon a mysterious black kitten during a routine forest expedition, unaware of its connection to the unsealing of a Dark God's tomb.