(Capcom's primary storyline)
"Sheva: This ship is huge. Do you think they're planning to use it to spread Uroboros?
The Tricell tanker was a ship owned by Tricell, Inc. and used by Tricell executive Excella Gionne and Dr. Albert Wesker. It was a large part of their plot to spread the Uroboros virus and cause a worldwide biohazard. Wesker's assault bomber was placed below the deck, set to take off from a specialized launchpad when the boat was at sea. The freighter's roof also had a specialized Satellite Laser Device.
"Excella: The preparations are almost complete. Then we can leave.
After escaping, Excella informed Wesker that their tanker was ready to launch. Wesker left his fight against Chris and Sheva, leaving them to deal with the brainwashed Jill Valentine and joined Excella. Chris and Sheva managed to get outside after saving Jill from her programming and witnessed Excella and Wesker boarding the ship, flanked by the Majini at the boat's entrance. As night fell, they managed to sneak on board. The BSAA agents wondered just how Dr. Wesker planned to infect the world with Uroboros as Chris noted that the ship was too big to use. They hurried across the freighter's deck, fighting past the hordes of the Las Plagas creatures and dealing with the locked security doors and crane traps and soon made it to the inner workings below the deck.
Wesker was safely in the command center above the deck, monitoring the entire vessel from the security cameras and viewing windows. Excella went down below deck to gather and organize the viles of PG67A/W for Wesker. Cornering Excella in an experimental room containing the Progenitor Virus flowers, Chris and Sheva demanded to know where Wesker was and held Excella at gunpoint. She casually grabbed her two briefcases of the serum and ran for a door, dropping one of her cases as Chris and Sheva fired at her. She locked the door behind her, but allowed Chris and Sheva to attain the serum necessary to defeat Wesker, though they are unaware about this at the time. As Wesker watched Chris and Sheva in an elevator from a camera, he mused that they would not get much further.
Wesker remembered back to his final encounter with Oswell E. Spencer and felt confident that he now had the "right to be a god" by reshaping the world with Uroboros. When Excella regrouped with Wesker in the command center, carrying her remaining case of PG67A/W, she injected him with a dose so his superhuman strength would keep in balance. He betrayed his partner by injecting her with Uroboros and sent her to the deck below near the approaching Chris and Sheva. The two came to an opening on the freighter's deck and saw a pile of Majini corpses from the Kijuju village. Greatly puzzled at the setting, they spotted Excella groaning in pain behind the bodies who Chris questioned.
Excella sadly said, "Why? When I did so much. All for you." amidst her agony. Wesker called out to the group over the P/A system, saying that Uroboros would soon create a new world for him to control. He pointed out that Uroboros was rejecting Excella and she was of use to him for one more task. Uroboros Aheri consumed her body and grabbed all of the Majini corpses on the deck. The monster quickly grew to massive size, roaring loudly and causing an echo across the large ship. It also caused major internal damage, causing a fire in the engine room. Chris and Sheva quickly ran along the ship's walkways as the beast's tentacles tried to crush them. They soon made it to safety inside the ship, but they would not be safe for long.
The beast managed to tear through the tanker with little effort and would have killed the duo had they not reached the bridge which was above the monster. From the viewing windows, the beast could be seen covering the entire deck and continuing to grow. It was clear that the creature would destroy the boat if left unchecked. Chris and Sheva made it to the roof after learning that a special satellite laser was placed there. The beast soon grew larger and reached the roof, attempting to consume Chris and Sheva. After several shots from the satellite's targeting system, the beast finally died and was frozen into a large mass of tentacles. They went back into the bridge where an alarm was going off because of the ship's damage. The freighter would eventually sink.
From a security camera, they saw Wesker preparing to launch his stealth bomber which he would use to spread Uroboros. They also found out from Jill that the viles of the serum that they collected earlier are in fact the key to stopping Wesker's superhuman abilities. Fighting past the last of Wesker's Majini and creatures, they soon located Wesker, overlooking his bomber from a platform. Engaging the two in a lengthy battle atop the launch pad after it rose from under the ship's deck, Wesker was soon weakened by the serum injection and decided to leave them on his slowly sinking tanker. He escaped to his bomber which was about to take off. Chris and Sheva managed to get on as the plane took off from the freighter's deck. The bomber flew into the air, preparing to launch Uroboros into the atmosphere and the tanker was left at sea where it eventually sank.