In Episode 5, the team from Namidome Industries grapples with the aftermath of their earlier actions and the ongoing challenges posed by the giant beasts. Tetsuro Okino, who has returned from his disciplinary leave, immediately finds himself at the center of the action.

The episode begins with a tense meeting at Shiota Bio, where Okino and his colleagues present a report on a giant beast they had previously sent for analysis. The results are inconclusive and yield no new insights about the creature. However, a piece of algae found on the animal sparks the impetus for a new investigation.

Arumi Nikaido remains focused on her mutated dog Shiro, who has now been identified as a giant beast. Nagisa Mizuhara, a researcher from Shiota Bio, approaches Okino and Nikaido with a risky proposal: using a GPS-equipped mouse to track the mutation process in real time, in hopes of uncovering the cause of the mutations.

Meanwhile, the company faces staffing issues. Ginnosuke Muto is hospitalized recovering from an injury, and the company is offered a new intern from Shiota Chemical, who brings a boat license and top-tier university credentials.

The team decides to prioritize investigating Hokujin Lake on Ryugan Island, where the algae blooms suspected to be linked to the mutations may be occurring. Okino and Nikaido release the GPS-equipped mouse near the lake to gather data.

While traversing the forest, Okino stumbles upon an unexpected swamp area and recognizes the danger of toxic gases in the vicinity. In a desperate situation, he cleverly uses a fallen tree to escape the quicksand-like peril, demonstrating quick thinking and resourcefulness.

The episode ends with a sense of urgency as the team realizes that a major threat looms if the giant beasts and toxic gas are not contained.