I really think that the author made a very smart move with the time travel shenanigans to not generate more confusion. Just "delete" the past nikaido and continue with the other one that traveled back, but with the changes done on the past.
Let's say she can use her magic 3 more times. If she comes to use it in the future and then her past self reaches that said point in the time line, can her past self still use magic 3 more times?
Let's say she can use her magic 3 more times. If she comes to use it in the future and then her past self reaches that said point in the time line, can her past self still use magic 3 more times?
I think the most logical thing here is for the box to be synchronised, so that it doesn't matter when or wich Nikaido uses it, the countdown is the same
So now, objectively it should left only one shot in the box since future devil Nikaido had to use one travel 🙊