Kartana is probably based off of a paper katana, namely Kusanagi-no-Tsurugi, a mythical sword in Japanese mythology. Either way, it is a very likely to be a type of origami.
While Kartana may be regarded as tiny and not powerful, however, it is highly dangerous due to the fact that it could cut anything due to being infinitely sharp and thin. This has been displayed in and incident in which a Kartana cut down a steel tower with one stroke, probably without effort.
Just as how certain other Ultra Beasts resemble human characters in the game, Kartana bears some resemblance to Gladion, with yellow growths on its body similar to Gladion's square cuts of hair, as well as its poses and its body resembling his jacket.
Kartana appears to be based on an origami sculpture. Its Grass type could be based on the Kusanagi-no-Tsurugi, a famous sword in Japanese mythology, as well as samurai katana blades, known for their sharpness.
Kartana may be a combination of katana, cartolina (a type of art paper) and art.