How best to send parcel to Japan?

Hi. I did a bit of searching around but I couldn't find anything that answered in a manner that made me confident I had the facts. My girlfriend lives in a dorm in Tokyo, I have a package maybe the size of a shoebox I want to send to her from the UK. I have read Royal Mail's guide (http://www.royalmail.com/japan) but it doesn't seem clear who will deliver it in Japan, and more importantly what will happen if my girlfriend is not home at the time of delivery (which is very likely). If Japan Post attempts delivery but she is out at the time, what will happen? Could anyone please help clarify this or suggest alternatives? UPS, etc? The package is not of great monetary value, but it is important that it reaches her. What is my best option?

Sorry for the potentially stupid question and thanks in advance for any advice.

Once the parcel reaches Japan, it will be handled by Japan Post. If she is out when a delivery attempt is made, they will leave a note informing her and asking her for instructions for re-delivery. She will be able to specify a date and time slots (like 9 - 12, 14 -18, 18 - 20). If you want full assurance, you can go for the tracked and signed (you can track the parcel all the way through), check the pricing.

Most importantly, make sure you have the correct address; it should be of the form

Name
Building name, room number
Building address
City, prefecture, post code
Japan

e.g.,

Hanako Yamato
Japan House 123
Ginza 12-3-4
Chuo, Tokyo, 123-4567
Japan

I also live in a dorm with mostly foreign students and I regularly receive mzil which was not for me due to the sender getting the address wrong...

Royal mail will send to JP Post, JP Post will deliver to your girlfriend's dorm.
But sometimes JP Post asks the other courier companies to deliver instead of JP Post because of busy.
When JP Post visits the place printed on the parcel, they will leave a note with phone number for re-delivery. She can phone to the number and ask for re-delivery day and time.
Or you can send it to the closest JP Post office where she can visit and pick up the parcel while the post office is opened without any extra charges. JP Post offices will keep the parcel for 10 days.