Kartana are bizarre, animate seed pods resembling humanoids folded from paper. They can levitate slightly through absorption of Ultra Energy from Necrozma-based sunlight, and they compensate for their weight by catching the wind on their paper-thin bodies. They possess muscle-like fibers that allow them to move like animals. Though they are almost identical to the muscle structure used by more familiar motile plant Pokémon, Kartana's tissues contain notable quantities of malleable metals such as copper, gold, and aluminum. Though it is composed mostly of a tough papery skin, several parts of its body are covered with copper and gold foil, thought to be for display or intimidation of rivals and predators.
The aperture on the front of its head serves as a mouth, and it uses it to ingest water, fruit, minerals, and meat. It no longer relies on photosynthesis for energy. It regurgitates material it can no longer use for nutrients. The back of the aperture, colored yellow, contains complex photoreceptors, allowing it to function as an eye. Tests on captive specimens show that Kartana struggle to perceive blues and purples, likely due to their vision being filtered by the yellow surface of the organ. Kartana have been noted to be quite expressive, shifting their four "jaws" to emote.
Kartana are born from the kami-trees that make up the forests of their homeworld. These trees are part of an Ultra Forest-native family that has very high metal content in their tissues. The family is flawlessly adapted to living in metalliferous soils, which are incredibly common in Ultra Forest. Kami-tree bark is tough and can be harvested for small amounts of iron and copper, while the leaves are incredibly sharp and foil-like in texture. Kami-trees also produce a latex sap that contains large amounts of cobalt and nickel, giving it a bluish-green color. When they pollinate and begin to grow seeds, the bud resembles a Kartana's face in green. As the pod grows, chlorophyll drains from the leaves as new ones grow to form Kartana's arms and legs. Kartana begins to express conscious awareness at this point. Next, gold and copper will begin to collect on the surface of the leaves, providing the Ultra Beast with its distinct coloration. Once it is fully grown, the Kartana will fall away from its stem and begin its independent life.
A Kartana's seed is very flat and positioned just under a copper foil cover on the chest. A Kartana's primary purpose is to protect its seed, and as such its primary weapons, its bladed arms, are positioned directly over the seed cover. Kartana have a long lifespan despite their biological purpose. Rather than plant themselves immediately, they live freely in the woods, challenging each other to duels. Their seeds can be viable for centuries, long after the Kartana has ceased to live. A Kartana can remain mobile for sixty or seventy years, and remain conscious for an additional twenty after that to pass on their knowledge.
Though highly intelligent, Kartana are monomaniacally focused on sharpening their bladed bodies and honing their swordsmanship. They rarely if ever attack unprovoked, and the sharp edges all over their bodies often make short work of would-be predators. Only very large opponents and those who threaten their seeds are met with active hostility. Kartana communicate amongst themselves in layered hissing voices, which show signs of being a complex language. They routinely challenge one another to sword fights, slashing with their arms and dodging gracefully in the air. Sometimes, a Kartana duel becomes a fight for survival. Kartana determine the quality of their seeds using their swordsmanship. They possess strict, structured societies where the strongest and most talented Kartana blade masters are those who get to plant themselves in the best locations. They adhere to a strong code of honor, and the winners of duels possess the most authority. The most lowly Kartana, after losing enough duels in a row, often drown themselves in dishonor to allow the more skilled to live. Those who go rogue and seek out places to germinate anyway are hunted down by core Kartana societies. When captured, these outlaw Kartana have their arms and legs sliced off and are pinned to tree trunks for the remainder of their lives.
Clans of Kartana have bonded with humans over the practice of kendo and kenjutsu. Kartana have adapted the ancient human art form to their own needs and taken it to absurd new heights with their extremely sharp arms. While humans practice on bamboo stalks, Kartana practice on stone and steel. These techniques are passed down to future generations, allowing Kartana to defend themselves from larger and larger threats and even shape the landscape to their liking. Portions of the forest have developed distinct zig-zag branches from some clans' obsession with diagonal lines. The Kartana will restrict and direct the growth of their own brethren to form these unusual shapes in their branches. Some clans have carved out magnificent atria and clifftops from the sides of mountains using nothing but their arms. Current theories strongly suggest that Kartana's obsession with skill and swordsmanship has encouraged them to develop their own culture surrounding it, and that their societal development has been accelerated by interaction with humans. Kartana seem to enjoy their human-inspired art forms, and researchers are advised to observe human-friendly clans for continued cultural osmosis.