This is an oddball one, for sure, but:

There’s this Blender/SFM video by the artist Evilbanana with an anthro, male-appearing Eevee alone in the woods, riding one of their favorite toys. But when they cum for the first time, they begin to evolve into a Leafeon and now their body is a lot more shapely and feminine - but still they have their dick and it’s even a bit bigger. So they keep enjoying themself, exploring their new body, and eventually cum again.