In every single region, the starters have always had some kind of theme or something in common. Here are some examples from Bulbapedia, and some I made up on my own.
Gen 1-. Each one of the starters was a reptile or at the very least, had reptilian features. Gen 1 focused mainly on genetics and science with Pokemon like Mewtwo, though the starters had something as well. Bulbasaur’s plant would grow larger as it evolved; Charmander’s final evolution was a dragon, and Blastoise had cannons on it’s back.
Gen 2-The starters didn’t have an extra typing and maintained this throughout evolving; Meganium was a pure Grass type, Typhlosion a pure Fire type , and Feraligatr a pure Water type. This was done to fit in with the traditional feel of Gold/Silver/Crystal.
Gen 3- The starters were more closely related to nature. Treecko was based upon a wood gecko and only lived in forests (and Sceptile is known as the Forest Pokemon), Torchic is a fire type because chickens need warmth to hatch, and Mudkip was partially inspired by the mudskipper, which made sense because it becomes a Water and Ground type.
Gen 4-Each starter’s final evolution was based on a mythological being. Torterra was based on the World Turtle; this makes sense considering that grass is a part of nature, and nature is a huge part of Earth. Infernape was based upon Sun Wukong of Journey to the West , and according to Bulbapedia, might have also been based on the Varana, who were a race of ape-like humanoids in Hindu mythology. An example of this is Hanuman, who was granted fire immunity. Empoleon was based on Poseidon, the Greek God of the sea. The Steel typing may have come from Poseidon's Trident.
Gen 5- One thing that I’ve personally noticed about the starters is that their design has a type of cultural design to them. Serperior’s design is based on French royalty, and its name is a combination of the terms serpent and superior. Emboar was based on a soldier in The Romance of the Three Kingdoms, a historical Chinese novel. In addition, Ken Sugimori confirmed that the Tepig line was designed in a Chinese style. Samurott is based on the samurai, who were very strong Japanese warriors who were members of the military; it also has some traits of a Japanese fan, which is pretty deadly.
Gen 6- The Starters are based on classes in a typical RPG. Chesnaught is the warrior class, fitting with its name and type since warriors are the strongest physically. Delphox is based on the wizard class and this is supported by the fact that it carries a wand around as well as having a robe( or dress). Greninja is based on the thief class, who is known for delivering strong attacks at a high speed. Its tongue is also long enough to function as a scarf.
Give your thoughts below and take as much time as you need to answer. What do you think the theme behind the starters will be?