Overnight Train Seat Reservation

Hi!
My sis, my friend and I will be arriving to Japan on July 31, we will activate our JR Pass on that day. However, we want to take an overnight train from Tokyo to Himeji (Sunrise Seto or Izumo). Can we reserve seats before arriving to Japan and activing our JR Pass?

The Sunrise trains have no seats. They have only berths (not fully covered by the Japan Rail Pass) and carpet compartments (fully covered by the Japan Rail Pass).

It is not possible to make reservations from outside of Japan.

Even if you have a friend or agent in Japan who can make a reservation for you, he/she won't be able to make these reservations for free because the activated Japan Rail Pass is needed for free reservations.

So, considering the relatively high risk of the carpet compartments being sold out on the day of travel, I recommend to avoid using the night train on the night of arrival or have a backup plan.

I am afraid the chance of sold out is big. For back up, you can take a train from tokyo to Nakaoka(長岡). At Nakaoka, there is a night train leaving for Osaka at 23:54. http://ekikara.jp/newdata/detail/1301153/43059.htm
Sunrise has become so popular these days. I would highly suggest a back up plan. By the way, this night train is called Kitakuni. It has only seats as oppose to the carpet nobinobi of the Sunrise.

Just to clarify, the station that lester mentions 長岡 would be written as Nagaoka in romaji. Personally, unless you are really set on taking a night train, or have some fondness for trains, then the Nagaoka route would be quite a detour just to catch a night train (up to Niigata and then back down to Osaka). Rather, why not just take a late hikari train, and stay in Osaka or Himeji. You can easily find cheap hotels in that area.

But if the point is to travel at night, and thus save sightseeing time and the cost of a hotel for a night, then I'd recommend the night bus instead. The fares are reasonable (~4000 yen), however you could easily find a hotel for less than the total bus fare.

My family has used http://www.123bus.net before with a good experience, but their online system seems to be down. Give them a call, they take reservations over the phone in English.