Resident Evil Gaiden is a Resident Evil video game featured on the Game Boy Color handheld console, and is the only one in the series so far which features Barry Burton as the main character. Although the word Gaiden suggests it is a "side story", the game is not canonical. It was developed by the now defunct company M4 Ltd.
The player takes the role of Barry, who is sent to complete Leon's mission. After discovering that everyone on the ship is a zombie, he finds a girl named Lucia. Barry runs to the deck which Lucia is on after hearing her screams and finds her being chased by a BOW which is the cause of the infection. After fighting and escaping the BOW, Lucia is kidnapped by the BOW
Barry then finds Leon unconscious and wakes him up. Barry and Leon cooperate to find Lucia. They find her being held by the BOW. They fight the BOW and save her before hearing an explosion. The ship starts sinking and fire is spreading throughout the ship. Barry runs to communicate with their headquarters to send them a helicopter while Leon and Lucia activate the sprinkler system.
After they activate it they hear Barry trying to sell the girl to Umbrella. Leon and Lucia find Barry threatens Leon with a gun to give him Lucia. Lucia goes with Barry and they both escape on an Umbrella submarine and leave Leon on the sinking Starlight. Leon goes to the engine room and damages the BOW before he destroys the ship and evidence of the outbreak.
In the submarine, the captain asks Barry to give him Lucia. He then finds that she has a parasite which will mature in 10 days and create a new BOW. He threatens Lucia and asks them to remove the parasite. The captain agrees and they remove the parasite.
The parasite manages to escape the jar which it is held and infects everyone on the submarine. They discover the BOW inside the submarine and they escape from it sealing it in the bay. Barry takes the submarine and heads to the near-sunk Starlight to find Leon. There they find Leon but it soon turns out that it is the BOW and it attacks them. After the fight they find the real Leon and they run over the deck where the helicopter is. There they fight the BOW before Leaving the Starlight.
The game ends with Leon's neck bleeding green from a small wound.
The enemies have bars under them where the A button is needed to be pushed to damage the enemies.