When Bell first lays eyes on the mermaid who applauded his performance against the Iguazu, his first thought is probably that he really shouldn’t stare at her for too long considering she’s topless. His reaction spooks her, but it isn’t long before Marie (no “Miss!”) is offering the finger she bit for him to suck on (her blood has healing qualities).
It also helps that Marie is friends with Xenos like Rei and Rido. I thought she might be the classic siren keeping Bell occupied while her Moss Huge ally picks of his party one by one, but it doesn’t seem to be like that. If anything, Marie is clingy because she’s lonely: her friends have wings and feet while she’s tethered to the water.
The Moss Huge doesn’t need Marie or anyone else’s help to create a huge shitshow for Bell’s party, led in his absence by Lili’s brains and Aisha’s brawn. It’s implied the Moss Huge has not only been stockpiling monsters but also influencing their movement patterns, such that the party ends up in the middle of a “pass parade”, when hordes of monsters are coming at them from all directions.
Despite overwhelming difficulty of avoiding getting flattened by the parade while still keeping the injured safe and mobile, Lili, Aisha & Co. manage to keep it together. Welf has to go through his magic swords like potato chips, but they’ve gotta do what they’ve gotta do.
Ouka proves masterful with his axe, while Makoto also whips out one of her new special techniques which splits a rampaging giant urchin clean in two, showing Aisha that she and Bell aren’t the only ones pulling their weight.
When Bell sufficiently promises neither he nor Marie will be killed if they leave the safety of her lagoon, she uses her song to locate a friendly monster and leads Bell back to his friends. When she runs out of water to swim in, Bell finally does what the show’s title has always promised and Picks Up a Girl in a Dungeon—and if it’s Wrong, I don’t want to be Right!
Even after their small victories and getting time for Cassandra to heal them, the monsters just keep coming in waves. Lili knows they can’t keep running without reducing the number of foes, so Aisha tells Haruhime that it’s time for her to unleash her Level Boost on everyone.
Hopefully that bullet isn’t used too early, and the resulting boost will keep the party afloat long enough for Bell and his new friend to arrive. But the fact that they’ve done so well without Bell for this long speaks to what a talented, coordinated, and resilient party they’ve become in a short time. You could say greatness is being forged in the watery crucible of these lower floors.