There are 47 prefectures in Japan. Prefecture is the subdivision of Japan. All municipalities, towns and villages belonging to one of the prefectures.
If there are 47 prefectures, there are also rivalries among prefectures. One of the samples is Yamanashi and Shizuoka. Yamanashi is located west of Tokyo and shares the boundary with Tokyo. Then, it is landlocked. Entire prefecture was the area of former Kai province. Then, definitely most famous person from Kai province is feudal lord, Shingen Takeda. Shingen had several fierce battles with feudal lord of Echigo province; current Niigata prefecture, Kenshin Uesugi at Kawanakajima in current Nagano prefecture. Yamanashi prefecture is connected with Tokyo by Chuo main line and Chuo expressway.
On the other, Shizuoka is not sharing border with Tokyo but it is not landlocked. The prefecture was composed by three former provinces; Suruga, Totomi an Izu. Shizuoka is located on the main route between Tokyo and Osaka, both railroad and expressway. Shizuoka has 6 Shinkansen stations which is after Iwate prefecture which has 7 Shinkansen stations.
Yamanashi and Shizuoka, which had few confrontations when feudal lords ruled their area but they share one of the most important thing in Japan, Mt. Fuji. If you ask each citizens, people of Yamanashi will say that Mt. Fuji belongs to Yamanashi but people of Shizuoka will say that it is Shizuoka's mountain.
There opinions are that Yamanashi has Fuji five lakes and it is common for people of Tokyo or foreign tourist staying in Tokyo to travel via Yamanashi to Mt. Fuji. However, Mt. Fuji can be seen when taking Tokaido Shinkansen, therefore more people can enjoy of the view of Mt. Fuji.
What is my recommendation? I would rather keep my mouth shut due to I do not want to be persona non grata of one of these two prefecturs!