Skeleton Knight in Another World follows the adventures of Arc, Ariane and Ponta as they travel a fantastic isekai world filled with monsters and strange creatures. Although Ponta is the first friend that Arc makes in his new world, little is revealed about what Ponta actually is.
Ponta can be easily recognized as a small green kitsune, which according to Japanese Shinto teachings is a type of kami (spirit or god) that can supposedly shapeshift into human form and is notorious for its mischievous behavior.
Ponta is a small green omnivorous kitsune that can be recognized by her distinctive tendency to yelp "kyu." She was first introduced in the second episode while Arc accompanied a young girl to collect flowers in the forest. Having noticed that the small kitsune had a wound on her leg, Arc decided to test his healing spell on the young creature. Recognizing Arc as a friendly person, the kitsune decided to accompany him on his journey. Taking into account the creature's absurdly fluffy tail, Arc decided to name her "Ponta" as a play on the Japanese word "tanpopo," which means dandelion. During their quest to pick flowers, the trio ran into a giant basilisk, which Ponta's reaction revealed to be the one who injured her in the first place.
The next episode introduced another exceptional ally in the series, Ariane Glenys Maple; a serious Dark Elf with a sweet spot for cute things who is dedicated to her mission of freeing her enslaved Elven brethren. Confusing Arc for a common bandit, Ariane attempted to kill him as he left a looted bandit camp. Ariane only stopped her flurry of slashes when she noticed Ponta climb up on Arc's back. It was here where Ponta was revealed to be a Ventu-Vulpis, or "Cottontail Fox" -- a spirit animal that can use wind magic combined with its fluffy skin to fly through the air, similar to a flying squirrel.
Spirit animals are not spirits -- rather, it appears to be a term used to denote a creature that is able to use "spirit magic." Unfortunately, spirit magic is only described as magic used by spirit creatures, so this creates a very unsatisfying and circular definition. The difference between monsters like the Basilisk and spirit animals seems to be the fact that spirit animals are more docile in nature and monsters contain a magic Rune Stone within their body.
The only other spirit animal introduced so far is a "whisper bird" or "whisper fowl," which appears to be an avian creature domesticated by Elves with the ability to carry human voices, functioning exactly like a carrier pigeon with a tape recorder. As revealed by Ariane, spirit animals are exceptionally elusive creatures who prefer not to interact with humans or even the more nature-tuned Elves. Furthermore, Elves are also capable of using spirit magic with the assistance of a spirit animal, implying that humans could do the same if they fostered their ability to communicate with spirit creatures.
Luckily for Arc, Ponta continuously serves as a method of de-escalating any given situation with a non-human. A great many non-humans in the world recognize the significance of a spirit animal choosing to follow an adventurer around, and seeing Ponta voluntarily accompanying him instantly clears Arc of representing malicious intent when he is confronted with a misunderstanding. For example, Ponta's presence deescalated the fight with Ariane, allowing him to become a trusted ally. It also gained him the trust of the mysterious furry-eared ninja who would have otherwise fought Arc.
In summation, not much is known about spirit animals. They are a very elusive and mysterious bunch of creatures that serve as one of the more interesting yet still tired tropes frequently found in the isekai genre.
