Evolution

The second condition requires that Eevee has to have a happiness value of at least 220. Happiness can be increased in a variety of ways, including:
✩ Giving it a massage/hair cutMassages (hair cut in HGSS) are located in Pallet Town (FRLG), Goldenrod City (HGSS), Veilstone City (DPPt), Castelia City (BW), Cyllage City (XY) or Mauville City (ORAS). There are also various places where you can check your Eevee's happiness in the different games by talking to certain characters: Daisy in Pallet Town (FRLG), a girl in Goldenrod (HGSS), a girl in Verdanturf Town (ORAS), a woman in Icirrus City (BW), Bianca via the Xtransceiver (BW2) and a girl in Laverre City (XY). In DPPt, there is also a Pokétch app that will show you the happiness levels by using the stylus to click on them.✩ Having it in your party
✩ Growing a level
✩ Giving it a Soothe Bell to hold
✩ Giving it vitamins
✩ Giving it certain berries
✩ Giving it certain Join Avenue items (BW2 only)
✩ Giving it juices from the Juice Shoppe (XY only)
Happiness can also decrease. If your Eevee faints in battle or you feed it bitter food, it will start to dislike you and take longer to evolve. This may be problematic depending on the level of your Eevee—Espeon learns the move Psybeam around level 20 (varies by game) and does not learn another psychic-type move by leveling up for a while. Just something to keep in mind!
The Sun Pokémon

Actual symbolism aside, the sun has some weaker connections to cats in my opinion. First, Leo is a lion constellation that is ruled by the sun. Some of the strong personality traits said of those who are Leos include being vain, dignified and loyal—arguably traits displayed by both cats and Espeon. While Pokémon have different personalities, Espeon is frequently shown exhibiting cat-like behaviors like grooming, having poise and even being somewhat aloof. Various Pokédex entries also say that Espeon is extremely loyal to trainers it considers worthy and wants to protect. Second, cats stereotypically love the sun. You will frequently find cats sitting by a window or laying in a sunbeam if they are given the opportunity to do so. Therefore, it makes some sense to make the Sun Pokémon a cat! Did Nintendo think about a possible connection between the sun, Leo and Espeon? Probably not. But it's interesting to think about!
REFERENCES:
1. Archetypal Symbols
2. A Dictionary of Literary Symbols by Michael Ferber
b a c k . c l e a r . f o r w a r d Morning Glory and its contents are © Samantha, however Espeon and Pokémon are © Nintendo and other rightful owners. Morning Glory is a part of AFTER-DEATH.ORG.