Reading this...reminded me a lot of ageswap au! (AUs where Mob is an adult and Reigen is a child, typically with Mob keeping his powers and Reigen remaining powerless.) It took me by surprise because I was expecting something more complementary to come from the Reigen-Tome dynamic, not a more conventional, "excitable apprentice kid and reluctant mentor adult" one. I liked the approach though, and I especially liked how it played a role in said buckling down on Mob Psycho's themes, with Tome learning she doesn't need psychic powers to lead a fulfilling and colorful life. I was itching for a Tome-Reigen-Serizawa-Dimple monster-of-the-week series once Tome learned to see ghosts and was presumably going to get psychic powers, but the route it went was far more consistent with the thematic road Mob Psycho had paved before it. I really loved the scene where Reigen admits to Tome he doesn't have any powers, and Reigen just being a Responsible Adult to these other confused teens outside of Mob in general.
I was spoiled on a couple of details about how it ends, but it still wound up being my favorite part of the entire manga. Reigen taking in an evil spirit was already so good, but then Mob coming to his rescue? Yes. Perfect.