When Pokémon GO first released, players eventually discovered a hidden nickname trick you could use to guarantee which Eeveelution your Eevee would turn into, instead of having it be a random evolution. The nickname Sparky would evolve Eevee into Jolteon, Pyro would evolve it into Flareon, and Rainer would cause it to evolve into Vaporeon.
Now with the release of Generation 2 Pokémon in the mobile game, players now have the chance to evolve their Eevees into either Umbreon or Espeon, and the nickname trick still applies. To evolve your Eevee into Espeon, players will have to nickname it Sakura. Likewise, naming it Tamao will guarantee the Eevee evolves into Umbreon. [Thanks, @PKTidal.]
These names are references to the Kimono Sisters in the who debuted in the Pokémon anime episode, “Trouble’s Brewing.” Tamao is the sister who had an Umbreon. Sakura is the sister who was a recurring character and had a standard Eevee in her debut episode that later evolved into an Espeon by “Espeon, Not Included.”
Pokémon GO is available for iOS and Android devices.