This is for my deconstruction of "sucked into a video game" story. I already have some new background characters to flesh out the world in the difference between video game and novella. My blank-avatar character can't do much of anything except advise. Someone needs to travel in time, might it be too much to insert a character that is closer to the level of the canon characters without overshadowing them?
Original character. @Smoke Z I'm a little lost as to why you'd even ask. Isn't the whole point that you do what you want with canon as your foundation, beyond that, whether you self-insert, go Mary Sue or introduce OC's is down to you. Surely if you write the OC well enough and give enough canon to tempt those interested in the fandom they'll go with it. Unless, of course, they are die hard purists.