An aquatic creature, Raiju invokes a Galapagos iguana and Crocodile in appearance and behavior. Broad shouldered, Raiju is heavily armored along its back and head. The "head" itself is a tripartite jaw that encases the creature's bioluminescent head for protection. Its feet are bent, enabling it to swim quicker through the water.
Raiju rose from the Breach along with Scunner and Slattern. However unlike other Kaiju that rose up to attack a city, the Kaiju rose to defend the Breach from Gipsy Danger and Striker Eureka. When the Jaegers arrive to bomb the Breach, it proceeds to stalk the Jaegers from the darkness during their approach to the portal. Raiju then assists Scunner in attacking Gipsy Danger, tearing off its arm from its body and snapping the arm in half before it can kill Scunner.
As he circles back for a second attack, Raiju ran head first into Gipsy Danger's sword, which combined with the speed at which he was swimming, bisects him from head to tail. Gipsy Danger initially decides to use what appeared to be one of the halves of Raiju to get into the Breach, but eventually abandons it, choosing to use Slattern's body instead to shield it from the Breach as it entered.
- Raiju's nickname during development was "Croc".
- According to Tendo Choi, Raiju is the fastest Kaiju on record (though this was before the appearance of Slattern).
- The appearance of Raiju, specifically its head, may be an homage to the Ultraman monsters, Gabora and Suppitol, who also have a protective false heads which they use to protect their real heads from their enemies.
- Raiju's name is a bit of a misnomer, as the Raiju of Japanese mythology was a creature with a broad range of appearances such as a wolf, cat, weasel, or fox. It was the companion of Raijin, the Shinto god of lightning.
- Raiju is a playable DLC character in Pacific Rim: The Video Game.
- Raiju is the heaviest Category IV known.