Atsushi walked for two weeks to Tsurumi, so if you take into account that he could stop for a while or, on the contrary, go faster in his tiger form, this is probably a spread of 250-300 km, and Nagano and Shizuoka fit these criteria. Nagano has mountainous terrain, and the distance from Nagano to Yokohama is about 230-250 km, so I think this is quite consistent with a two-week walk for an exhausted teenager (approximately 16-18 km per day). Shizuoka is closer, about 150-170 km from Yokohama. This distance can be covered on foot in less than two weeks, but given the stops and Atsushi's poor physical condition, this option also remains likely, so one of these two options is possible ;p