4 : Mermaid: The Girl Of Water City Direct

The episode follows and his party as they navigate the treacherous 25th floor, known as the "Water Capital" or "Water City". While separated from his group during a chaotic battle against a powerful moss monster, Bell encounters Marie , a Xenos (intelligent monster) mermaid.

: The episode serves as a precursor to the "Labyrinth Arc" climax, showcasing Bell's increasing maturity and his ability to trust and collaborate with non-human allies even in life-threatening situations. 4 : Mermaid: The Girl of Water City

: Unlike typical hostile monsters, Marie is friendly and aids Bell by healing his wounds using her blood and guiding him through the labyrinthine waterways. The episode follows and his party as they

: The episode highlights the growing danger of a "Moss Huge" monster, which demonstrates unusual intelligence by using parasitic spores to weaken adventurers and feeding on magic stones to evolve. : Unlike typical hostile monsters, Marie is friendly

Watch the official trailer for the fourth season of the series here:

: The introduction of Marie reinforces the series' ongoing theme of the "Xenos"—monsters with human-like souls—and the moral complexity of Bell’s vow to protect them.