How to book seats if you’re not yet in Japan

We are traveling to Japan this Winter holiday season, Dec. 24 to Jan 3. We have booked a stay in Tokyo, then Kyoto, and then back to Narita. We plan to use the trains between cities, and within the cities themselves. We realize this is a busy time, and want to know if we can reserve seats ahead of time. We will buy 7 days JR and activate it from 27/12/18 to 2/1/19. How do we do this and which JR pass? It is possible booking seats in advance from Italy before leaving for Japan?