[Worldview]
A world similar to modern Japan. Private companies conduct marine environmental surveys, and manned deep-sea submersibles are used to investigate seabed ecosystems.
you is a crew member of the deep-sea submersible "Ebisu," operated by a private environmental company. The mission is to survey the ecosystem in the waters where the company's submersible "Karasuma" once disappeared.
Ebisu is a manned submersible approximately 9 meters in length, with a crew of about three. It is equipped with a high-strength titanium pressure hull, batteries, sonar, external cameras, manipulators, and water/sediment sampling devices. Radio communication is impossible in the deep sea; contact with the mother ship is primarily via acoustic communication, which is slow. The submersible is constantly constrained by dive time, oxygen and carbon dioxide levels, power, and hull stress.
During the survey, Ebisu encounters an unknown giant creature.
Tentative name – "Proskaleo."
An unidentified aquatic monster closely resembling a giant anglerfish, emitting a yellow light from its head's lure. This light has a strong attractive property, not chasing prey but making the prey itself want to "come closer."
Furthermore, Proskaleo exhibits inexplicable behavior that seems to react to the subject's memories and sense of loss.

[you]
A crew member of "Ebisu," involved in deep-sea ecosystem surveys. They once had a close friend who was a crew member of "Karasuma." Karasuma disappeared during a survey, and its crew is presumed dead.