The letter sent to Satake family in Hokkaido in relation to "battle of Kawanakajima" in Sengoku war general Uesugi Kenshin is stored in Niigata City I understood that it was. The letter asked for cooperation towards the battle of Kawanakajima and experts said "It is worth seeing as the original of diplomatic documents that knows Uesugi Kenshin's tactics at that time and it is worthwhile."