Episode 9 of "Seijo no Maryoku wa Bannou Desu" Season 2 begins with Sei and Albert discussing the unusual size of a wild boar-like monster they encountered earlier, speculating that it might be connected to the miasma swamp in the mine. Albert notes that more and more monsters have been appearing in the area lately.

As Sei, Albert, Yuri, Wolff, and the knights venture into the mine, they face a onslaught of undead creatures. The group is determined to reach the miasma swamp, which they believe to be the source of the monsters. Yuri suggests an experiment to purify the miasma swamp himself, though he isn’t sure if it will work.

Sei notices the group’s injuries and offers to cast an area healing spell, even though she needs to conserve her magic for the swamp.

The group delves deeper into the mine and encounters even more undead. Yuri’s attempt to cleanse the miasma swamp proves ineffective, so she decides to try her purification spell instead.

In a tense moment, Sei falls to a lower level of the mine and is separated from the group. She reflects on her dependence on others and her role as the Saint. Meanwhile, Albert, Yuri, and the others search desperately for her and eventually find her near an exit.

The episode reaches its climax as the group discovers the main miasma swamp, guarded by an undead dragon. This revelation explains why the monsters weren’t fully eradicated before. The team engages in a fierce battle against the dragon while Sei prepares to cleanse the swamp. The episode ends with Sei successfully using her magic once again to save the situation, supported by her companions’ efforts to protect her.