Shinkai no Survival!

Geo, Pipi, and Dr. Kon descend in the Ammonite submersible to explore the deep sea, but methane bubbles damage the craft and cut off contact with Kay on the surface. With the submersible's energy running low, an encounter with a giant squid and a sperm whale separates Geo from the others. He is left alone in the darkness of the seafloor, surrounded by unfamiliar deep-sea life, while Pipi and Dr. Kon race to find him. Survival depends on understanding an environment where humans have little light, no breathable air, and almost no room for mistakes.