Pokemon Scarlet and Violet could get a new Eeveelution according to a pattern established by the anime

gamesradar.com:

A new Pokemon fan theory says we could get a new Eeveelution according to a pattern established by the anime.

The theory, which was originally posited by The Gamer, says that Pokemon Master Journeys may be hinting at a new Eeveelution appearing in Gen 9. According to the theory, every time a main character in the Pokemon anime catches an Eevee, it eventually evolves into a new form. This can be seen in the X & Y series that gave us Sylveon, Glaceon in the Diamond and Pearl series, and Umbreon and Espeon in the original series. 

The theory also notes Leafeon doesn’t exactly follow the pattern, but given taht it appeared in the games alongside Glaceon, it doesn't necessarily break the theory. It would make sense for the current series in the anime to feature the latest Eeveelution as it would line up with Pokemon Scarlet and Violet - which is set to release in late 2022. 

There is more evidence to support this theory though. As explained in The Gamer story, side character Chloe (also known as Professor Cerise’s daughter) joined the anime in its 23rd season Pokemon Journeys. She joined main characters Ash and Goh but was apprehensive at first about being a Pokemon trainer. This changes though when she meets an Eevee who had escaped an Eeveelution test facility just before.

The important part of this encounter though comes down to what happened to this particular Eevee in the Eeveelution test facility. According to the theory, researchers tried to evolve Eevee with various stones but none seemed to work. This leads the researchers to let Eevee go out and adventure with Chloe to 'find itself' but not without first telling Chloe that this Eevee has "chaotic DNA" - which sounds exactly like what a new Eeveelution would have. 

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