A tradition among FakemonMakers is to imagine our own Eevee evolutions! A complicated but satisfying exercise when you arrive at a result close to the official Eeveelutions.
This evolution of Eevee is of the FLYING type: Zephyreon
Its design is basic for this type, but easy to understand! Compared to other possibilities I found on the internet, I chose this simple appearance taking on a feathery and fluffy appearance for an Eevee glider.
I imagine it to be a Pokémon that doesn't like to be observed, living high up in the mountains, above the mountains, above the clouds, therefore far from prying eyes.
The reference object allowing Eevee to evolve is: the Winds Stone. Another reference to a Ghibli film "Laputa: Castle in the Sky", taking inspiration from the Laputa Flying Stone. (I admit, this is the only idea I found for creating a Flying type evolution item)
Ingame, the item “Winds Stone” is found in the same mountainous cavern as Larveetle and Scaragon.