Buying Shinkansen tix ahead of time

Hi,

I'd like to buy Shinkansen tickets from TOKYO to HIROSHIMA for my sister and myself ahead of time, just to be safe.

Here's the issue: I am an ALT here, and she will have a Japan Rail Pass. How do I purchase tickets ahead of time for the both of us? She arrives in Tokyo 2 days before we head to Hiroshima. We plan to leave Tokyo early 3/25... will this be an issue, or could I just wait until she is physically in Japan to buy the tickets?

She is a Japan Rail Pass holder, she doesn't need to buy a tickets, her Japan Rail Pass is her ticket.

However if you mean seat reservations then yes she needs a seat reservation too (which is free with her Japan Rail Pass).

You however because you don't have a JR Pass, you need to purchase the actual Shinkansen tickets and make a seat reservation (which can be done at the same time).

However, the problem comes with this:
She is a Japan Rail Pass holder so she cannot use the Nozomi Shinkansen (which goes direct to Hiroshima and beyond from Tokyo), therefor you need to limit your ticket as well to riding on the Hikari Shinkansen with one transfer at either Shin-Osaka or Okayama.

She needs also needs to be present with her JR pass to make the reservation, without it I'm not sure how you can make a free JR seat reservation, unless you wanted to pay for one.

Alternately you both don't need seat reservations and can opt for the unreserved seating section on the Shinkansen.

3/25 will not be a busy travel day. It should be no problem to make seat reservations the day before or even on the day itself.