You don’t have to buy JR East Pass before arriving in Japan. It can be purchased at the airport on arrival at Narita and Haneda airport, or from any major JR East Stations. In Tokyo, you can purchase the pass at Tokyo, Shinjuku, Shinagawa, Shibuya, Ikebukuro and Ueno station. If you would like to purchase from your travel agent in your home country, you can do that as well. If you buy the JR East pass in Tokyo you will need to show your passport as well as your return air tickets as evidence that you are in Japan for short stay. I do recommend that you take the JR East Pass if you travel more than 3 hours combined on Shinkansen. Travelling at least 3 hours on Shinkansen can easily cost 16,000 Yen. And if you add on your stay in Tokyo and travel using Narita Express, the cost can easily be covered.
JR East Pass.
Travelling from Narita airport to Tokyo is covered by JR East Pass.
Status board on Narita Express (NEX).
Hokuriku Shinkansen to Nagano. 1 hour 45 minutes on the fastest Kagayaki train.
Very long bullet train.
Selfie with Japan bullet train.
Japanese style notepad. JR East provide gift for those who travel long distance on Shinkansen train. You can collect souvenir or gift from each major stations that you reached using JR trains. More details here.