in the ttrpg system our DM created, every person is born under the "sign" of a certain pokemon. they're meant to have some connection with the person, but for pcs it's rolled at random— for npcs you can do whatever.
everyone has one but since only Psychics and Hex Maniacs can see them, not everyone knows theirs or even knows they exist. those two trainer types can also gain a skill that allows them to use a random attack from their pokemon at level 100, but you can nearly kill yourself with the recoil if it fails. the secondary use is that people with a legendary/mythical pokemon as their Star are the only ones who can actually catch them.
there's some extra rules to Stars based on pokemon with muliple formes:
Stars also cannot evolve.
other than that, they're pretty useless. i just like to go ham with their symbolism.
