Name & Origins"Espeon" seems to be a cross between ESP (extrasensory perception) and the eon suffix that all Eevee evolutions have at the end of their names. Similarly, its Japanese name, エーフィ (Eifi) is likely a combination of the words エスパー (ESPer) and フィール (feel). As Espeon is the psychic evolution of Eevee, both names are certainly fitting. ESP, also known as the sixth sense, is a type of psychic ability that can include things like telepathy, precognition (telling the future) and even clairvoyance and clairaudience (seeing and hearing spirits/ghosts). Based on Pokédex entries and Espeon's appearances in the anime and manga, it clearly has both precognition and telepathy. The "feel" aspect of Eifi may also represent Espeon's ability to feel minute changes in air currents and thus predict the future.
Espeon's design arguably has aspects of two different mythological creatures. A Carbuncle is a cat and dog-like creature said to be found in South America. They were rare and sought out for the beautiful jewel on their foreheads. Further, they were supposedly able to sense the feelings of others, especially feelings of greed. Carbuncle can also refer to a red colored garnet, which leads me to believe the stone in mythology was probably red. Espeon clearly has a red stone embedded in its forehead and is shown using it for attacks like Psybeam. This may be a reference to the Carbuncle emitting a bright light from the stone when it blinded those filled with greed. Sensing the feelings of others is another type of ESP and an ability of many psychic-type Pokémon like Espeon. Lastly, Carbuncle is a summon in many of the Final Fantasy games (like pictured to the left of this paragraph). I found it interesting how similar shiny Espeon (which is green instead of purple) looked to Square's depiction of Carbuncle!
Espeon also seems to have some features of a nekomata from Japanese folklore. These cat demons have a number of stories behind them, but the reference that seems to fit Espeon the most is the stories of regular cats turning into nekomata as they grow older. A person would be able to tell if a cat became a nekomata because it would have a split/forked tail. Nekomata have also been said to have powers similar to poltergeist activity in some stories as well. Espeon not only looks like a cat, but it also exhibits a number of cat-like behaviors in the way that it sits, sleeps and cleans itself. Espeon's tail is long and forks toward the end just like the stores of nekomata. Although poltergeist activity is often alluded to being a ghost phenomenon, it's actually usually psychokinetic energy of teenage girls. Therfore, the poltergeist activity said to be caused by nekomata could parallel Espeon's psychokinetic powers, too.
CounterpartAny dedication to Espeon wouldn't be complete without talking about Umbreon. Espeon and Umbreon are second generation Eevee evolutions that are frequently presented as a pair—as counterparts, really. Both require happiness in order to evolve from Eevee. The only difference is the time of day. While Espeon is the Sun Pokémon that evolves during the day, Umbreon is the Moonlight Pokémon that evolves at night. Espeon and Umbreon are like the sun and the moon in that they represent polarity, but are still connected through the means of evolution (time of day). I've discussed the various connections Espeon has to the sun here. As for Umbreon, some argue its appearance is based on the moon rabbit (namely its ears) as well as relating its golden rings to Egyptian lunar markings. Further, "umbra" is a term for the moon's silhouette during a solar eclipse. I thought this was particularly interesting because while the moon is illuminated by the sun's light, the moon also has the ability to block the sun. The solar eclipse could even symbolize that Espeon, a psychic-type, is weak against Umbreon, a dark-type! Somehow I doubt Nintendo put that much thought into their duality, but it's fun to think about.