"An everyday man gets thrown into the world of twilight thousands of years before the start of the plot. With immortality and incredible abilities. How will this man's presence change the outcome of the original story?" [ this is a slow-burn fanfiction; the MC is just trying to experience life and enjoy it, not to take over the world and rule from the shadows.] I do not own twilight or the characters of the twilight world, all that belongs to me are my own characters.
I feel like the story would be better if he was older or born in a different era like the real rihan. Then you still want to have the older sister relationship with satsuna too. sure tsurara might not be around but, she could be his and her daughter or something else. It would've given you more time to have trained. it would have given you more time to worldbuild it would have done so much if he was older of born in a different era like the real rihan. Heck I think the real yasaka could be about the same age as the real rihan. she could have been a friend. I just feel like you ruined your story having him be older. If you really wanted this just be the original character rikuo or don't have him be nurarihyon's kid