Kono Subarashii Sekai ni Bakuen wo! - Episode 12 [END] - Megumin Flowing Cape

Megumin's origin story became complete when she introduced herself to Aqua and Kazuma.

Yunyun and Megumin had devised a sneaky plan to defeat the demon trying to take Chomusuke away. But Yunyun wanted to protect the vulnerable Megumin from a dangerous fight. Megumin woke up late after Yunyun's sleeping spell wore off. Yunyun's strategy with her adventurer companions almost worked, but her paralysis spell affected her too. Sister Cecily's blessing and Megumin having two full days' worth of magic levels made her Explosion spell extra potent.

Yunyun challenged her eternal rival Megumin to a future contest, but she needed to go on a journey of self-improvement first. Megumin struggled to find a new adventurers' party until the fateful day she met Aqua and Kazuma. You know the rest of the story in Konosuba: Blessing.