In its home world, Opixinia is a scavenger. It roots around the seafloor with its clawed proboscis, feasting on the sludgy remains of long-dead Nihilego and Yolawis. Outwardly, it resembles ancient Earthling radiodonts of the same family as Anorith and Armaldo. Tissue samples show that it is made of substances native to the Deep Sea, but it is unclear whether this is because it is truly native or because it had nothing else to eat. There are a number of researchers who strongly believe that it is indeed a descendant of basal arthropods from Earth, and its altered biochemistry is simply the result of being forced to live in and adapt to an alien world.
Either way, it has survived well in Ultra Deep Sea, for their populations are large and healthy. Like other Fairy-types, Opixinia are playful and mischievous, chasing each other around the reefs and playing gentle pranks on one another. They live in pods of around eight or nine individuals, and the larvae are raised communally. It is quite common for multiple pods to congregate into vast schools thousands strong. When schooling events occur, adult Opixinia select mates from other pods using a series of small games. Once individuals settle into mated pairs, they either join their mate's pod or leave together to start a new one. Opixinia are doting parents, evidenced by the mother gluing her eggs to her belly with a special resin. If her clutch is too big, she will glue the rest to her mate or an infertile volunteer. Opixinia mate for life and can recognize their children long after they have matured.
Opixinia are fearless and curious. They will approach squad members to study them, making them incredibly easy to document up close. Individuals are known to test unknown objects with their probosces and ribbonlike antennae. Once they realize that humans are no threat, they will happily play with them and accept treats and petting. A large, healthy pod is currently being maintained by the Laboratory Research Division, giving researchers an incredible insight into their surprising intelligence and complex social behaviors. The pod is reproductively active, so additional specimens are to be captured to maintain genetic diversity and mature young are to be released during schooling events to allow them to find mates in the wild.
When a colony of Nihilego is in grave danger of being devoured by Yolawis, Opixinia become their favored target. Opixinia's typing gives them an incredible advantage against Yolawis, and their minds are powerful enough to withstand short-term exposure to Yolawis' psionic field. When Nihilego attach to Opixinia, the latter's flight instinct is overridden by fight, and the parasite colony assembles a swarm to bite and slash the Yolawis to death with powerful STAB Bug-type moves. The altered state of mind caused by the neurotoxin protects the Opixinia from psychological damage, and once the threat has been vanquished, the Nihilego order Opixinia to devour every trace of the Yolawis. This is where Nihilego earned its title as "Symbiont"; its possession of Opixinia is entirely beneficial to both parties, protecting them from predation while simultaneously feeding them enough to last every participant a few days. It is for this reason that Opixinia do not flee in terror from Nihilego like other residents of the Deep Sea. They simply mind their own business, and if the Nihilego commandeer their bodies for protection, they have nothing to fear.