PLOT
Following a recently failed quest, Kazuma Sato, Aqua, Megumin, and Darkness are visited by Yunyun. Yunyun explains the letter from her father telling her to have a son with Kazuma to make their child avenge the people of Crimson Demon Village, her and Megumin’s hometown, when they get destroyed. However, they discover that the part asking for Yunyun to have a son with Kazuma was actually an excerpt of a classmate’s fanfiction that was accidentally sent with the letter. Still, Megumin decides to check her village’s condition, so Kazuma’s party asks Wiz to teleport them.
After defeating a group of female orcs and an army of goblins with Yunyun and Crimson Demon Clan members’ help, Kazuma’s party arrives at the Crimson Demon Village and visits Yunyun’s father, who admits to exaggerating the aftermath of the attack on the village by one of the Demon King’s generals named Sylvia. In fact, the Crimson Demons have been effortlessly repelling all Sylvia’s attacks so far. Afterward, Kazuma’s party visits Megumin’s house and meets her family, who become interested in Kazuma for his fortune. The following day, Megumin shows Kazuma and Aqua around the village, visiting her school and the storage building that holds the Mage Killer, a weapon capable of destroying the world. They later find Darkness fighting Sylvia and her army, but Sylvia retreats after learning of the defeat of Verdia, Vanir, and Hans from Kazuma. Later that night, Sylvia manages to take Kazuma hostage and brings him to the storage building to steal the Mage Killer, but Kazuma traps her inside and reunites with his party. She then fuses with the Mage Killer and begins destroying the Crimson Demon Village. Kazuma’s party finds a high tech rifle that was built to counter the Mage Killer and uses it to kill Sylvia.
A dying Sylvia encounters Verdia and Hans in the afterlife and fuses with them to be revived as a giant monster. Wiz and Vanir arrive at the village for a business trip but end up joining the fight. Wiz collects the Crimson Demon Clan members’ magic and transfers it to Megumin and Yunyun, while Kazuma seduces Sylvia to buy them time. Megumin and Yunyun destroy Sylvia with their combined powerful attack, with Kazuma also perishing. Afterward, Kazuma is revived and returns to Axel with his party. While on a picnic, Megumin asks Kazuma to put her experience points into another skill to be a useful mage without relying on her Explosion magic. She casts her final Explosion skill as a farewell but finds it much stronger than usual, realizing that Kazuma disregarded her request and put the points on it instead. As they meet up with the others, the smoke from the explosion forms the shape of a heart in the sky.
