Subnautica

Roughly 1,000 years prior to the game's events, an alien race known as "the Architects" begins investigation of the ocean planet 4546B for a cure to the Kharaa bacterium, which has devastated their civilization. They discover that the Sea Emperor Leviathan species naturally produces "Enzyme 42" in its digestive tract, which makes the species immune to the bacterium. The last of the species is too old to produce the enzyme in sufficient quantities, and attempts to force its eggs to hatch (to extract the enzyme from her young) are unsuccessful. As the Architects grow desperate for a cure, they attempt to extract the enzyme from a related species, specifically the Sea Dragon Leviathan. This leads them to abduct a Sea Dragon egg for research. Following the abduction, an adult Sea Dragon Leviathan attacks the research facility where the egg is being held in an effort to retrieve it. This attack causes the facility to collapse to the sea floor, resulting in the Kharaa bacterium being released into the ocean. With the situation worsening, and the containment breach inadvertently infecting the ocean with the Kharaa bacterium, the Architects place 4546B under quarantine while forcing the remaining Architects to upload their consciousnesses onto cache data hubs.
Centuries later, the spaceship Degasi crashes on 4546B while scanning it for minerals. Three of its crew members survive for a few months on the planet. 10 years later, the Alterra Corporation's spaceship Aurora crash-lands on 4546B while attempting to locate the wreck of Degasi. The player character Ryley Robinson, who is the Non-Essential Systems Maintenance Chief, is among those of the Aurora crew to eject in escape pods. He is knocked unconscious during atmospheric entry, and finds himself to be the sole survivor by the time he wakes up. He is contacted by the trading ship Sunbeam, responding to the Aurora's SOS. When the Sunbeam attempts to rescue Ryley, it is shot down. Ryley investigates and discovers that the weapon responsible is the Architects' Quarantine Enforcement Platform, and that it will continue to shoot down any ship it detects attempting to enter or exit the planet's atmosphere, to prevent the spread of Kharaa. Ryley attempts to disable the weapon; the control panel detects he is infected with Kharaa and, as such, denies his input.
Ryley ventures deeper into 4546B, learning of the Architects' history through exploration of their facilities. He discovers the last living Sea Emperor, still captive in an Architect containment facility, who can communicate telepathically. Ryley activates a teleporter inside her aquarium to allow the Leviathan's young to leave; in exchange, she provides Ryley with the recipe for an enzyme that will allow her eggs to hatch. Ryley uses the enzyme to hatch the eggs; the Leviathan young release large quantities of potent Enzyme 42 into the environment, curing Ryley and halting the bacterium's spread throughout 4546B. Finally at peace, the ancient Sea Emperor bids Ryley farewell and lays down to die.
A cured Ryley can disable the Quarantine Enforcement Platform, construct an escape rocket based on blueprints recovered from the Aurora wreck, and leave the planet. In its final telepathic communication, the Sea Emperor poetically compares itself with Ryley.