This is not gospel, this is just my opinion and how I categorize my own creations! You can define these terms, use or not use them, however you want to! I’m just putting this here for my own reference mostly
A persona is explicitly for self insert purposes.
These characters do not have a role that alters the lore of the existing canon.
They can interact with characters, so long as it is done in an inconsequential way. If desired, the persona can have their own subplot to be resolved.
It’s absolutely possible to have a persona for your own original work.
Personas exist as different versions of the self. No need for lore, sometimes a different costume is enough to establish the self as a different sona
When the persona has a larger role that impacts the canon line of events, they cross into OC territory.
Persona Examples
The Farmer, from Stardew Valley
Animal Crossing Player Character
Character based on the self, but designed for the world. “Me if I were a stand user.”
Any character who is based on the self but does not change the end goal of a preexistent plot
OC Examples
A Stardew Valley OC would inherently change playable canon. If your SDV persona is dating Alex and Alex is no longer a viable Romance Route, then your persona is an OC
A yokai watch NPC who has a cool yokai and directly helps Nate do XYZ, explicitly influencing the plot’s course
A character that may or may not be based on the self that is more plot significant than not.
Plot significance doesn’t exist on an easily measurable scale so it’s a loose metric, deliberately
Mary sues don’t exist btw the point of an OC is to have fun and be self indulgent. Enjoy your blorbos and let them live and love as freely as you would do so yourself.