From what I know, Japan is really an expensive place to live, especially in the cities. Unless Mirai's relatives are in the same city as her coach, I don't see her saving money training in Japan.
Originally Posted by Victura
Given that Nagasu is ethnically Japanese, it's reasonable to assume that she had relatives to stay with in Japan, not to mention that was meant to be a temporary situation. Different than finding a new place to live permanently and all the costs associated with that.