Not much is known about the planet Koppai other than it having a single moon, and that it is about 279,000 light-years away from PNF-404. This kind of distance suggests that Koppai is located outside of the Milky Way Galaxy, as it is only 100,000 light-years long. This implies Koppai (and maybe Hocotate) could be situated in one of the many "mini galaxies" clustered around the outside rim of the Milky Way galaxy. Its surface is never seen or described in-game, but the opening cutscene seems to imply that the planet has a very thick atmosphere, covered in large masses of clouds.
Koppai, just like Earth, appears to rotate on a tilted axis. However, its moon appears to revolve around it vertically, revolving from North to South counterclockwise. This type of orbital pattern has never been observed in any real life celestial bodies.
According to Brittany, the gravity on Koppai is roughly ten times stronger than on PNF-404, and the oxygen levels are about three times higher on PNF-404. The stronger gravity suggest from an astronomical standpoint that Koppai is about ten times larger in mass than PNF-404. Accordingly, if PNF-404 is assumed to be Earth, Koppai would have an atmosphere that consists of roughly 7% oxygen. Brittany hypothesizes that the higher oxygen ratio is what allows the life-forms of the Pikmin Planet to grow to such, comparatively, large sizes. It is assumed that the giant insects that lived in the Permian only grew to their size due to the greater amounts of oxygen in the air during that time, which would support her theory.
Nothing is known about life on Koppai other than that it's inhabited by sentient life forms known as Koppaites, which are very similar to Hocotatians. Hocotatians and Koppaites seem to speak the same, or very a similar language, as throughout the events of Pikmin 3, they communicate effortlessly. They also seem to have a very limited diet, seeing as how fruits are favored over vegetables, as seen in a conversation between Brittany and Alph on the Drake.
One other form of life on Koppai is suggested to heavily resemble Earth ducks, seeing as rubber duckies such as Charlie's are normal to Koppaites. Although their appearances and biology are not known, it is known that Koppai has dogs and/or ducks: Charlie's pet is stated to be a dog in the US version, whereas it is stated to be a duck in the European version. At one point, Brittany also mentions geese on Koppai. Finally, it appears that reptiles are known to Koppaites, judging from Brittany's notes on the Scaly Custard.
Prior to the start of Pikmin 3s events, it is known that Koppai has quite an expansive population, which lusts heavily for eatables. Its sub-par planning of the production necessary to sustain such a lifestyle eventually lead to a food shortage. Pikmin 3's storyline starts with three explorers being sent out on a mission to find a planet with food, so that it may be retrieved to stop the hunger problem.
If the player completes the game without all fruits, it is made unclear whether the Koppaites pull throw with the limited food supplies recovered by the game's leaders. Completing the game with all fruits, however, shows how Koppai prospers as a civilization and manages to change their lifestyle in order to prevent future disasters like this one.
The technology on Koppai is likely similar to that on Hocotate, as several of the communication mediums used in Pikmin 3, such as Data Files and the KopPad, are compatible between Koppaites and Hocotatians. An interstellar bazaar is also known to exist, selling space-travel hardware that is bought by both Hocotatians and Koppaites.
Koppai is also known to have the necessary technology to construct unmanned scouting probes, called SPEROs, as well as ships capable of speech, such as the Drake. There are distinct roles for engineers and botanists on Koppai – Drake and Alph are engineers, whereas Brittany is a botanist. These suggest that technology on Koppai has at least passed a point where such job title distinctions are necessary for everyday life and cultural growth.
Other, minor objects are also known to exist: Brittany mentions crayons on her notes on the Portable Sunset.
It seems that Pokos are a universal currency in the Pikmin universe, as Koppai is also hinted to use them. Pikmin 3's Collect treasure! stages have markers for a point value, labeled with what appears to be a Poko.
Due to the fact that Koppaites have it "written into their DNA to never stop eating and never stop to plan", it can be assumed that they have a very weak government, or one that may be consumed by anarchy. However, Brittany mentions elections when speaking to Alph, meaning there must be some sort of president or mayor on Koppai.
The following characters in the series are known to be from Koppai:
Relations with Hocotate
A Data File left by Olimar and later found by the leaders mentions Hocotate. Whichever leader is active at the moment the file is retrieved will then recall that Hocotate is a planet a few solar systems away from Koppai, with a population that is interested in monetary gains rather than food. Olimar is simply referred to as a man that must love his family very much or has a lot of time to kill. While a vague description, the idea that the people of Hocotate and Koppai are unfamiliar with each other or even different species entirely seems unlikely. Given the leaders' equipment in-game, it seems that oxygen is as poisonous to them as it is to the Hocotatians, which, apart from the obvious physical similarities between the two peoples, shows a further common feature. As mentioned above, the technology used between the two planets is also similar.
- The name "Koppai" comes from Nintendo's founding name, "Nintendo Koppai", back when they were still a card company.
- Originally, the source code on the Pikmin 3 Japanese website could be examined to reveal some lines of text: "Brittany, botanist on behalf of Coppa Lee Star", whereas Alph and Charlie were both listed as "on behalf of Koppai Star". Because "star" can translate to any celestial body, many assumed this meant Brittanty was in fact from Koppai's moon, which was thought to be called "Coppa Lee/Koppali". However, it was later discovered to be a mistranslation.
- Although not much is known about the planet's past, it appears that Koppai did at one point have a medieval period similar to ours, as Alph uses "double-edged sword" as a metaphor in a report.