My sugestions and you can do all or some. I will try to put them in order of importance. This applies to you and your friend.
1) Call home, talk to a family member. Hearing a familiar voice does wonders.
2) Remember why you went to Japan in the first place. Look on line and ask hotel staff for things to do, areas to check out. Even if you aren't into shopping or bars, there are tons of things to do. There are arcades, amusment parks and tons of things just to look at. I recomend Odaiba.
3) Keep you friend busy, plan something that will last later in the day and/or start earlier. Get up early, open the curtains, make noise and wake your friend up. If you have to, DRAG your friend out.
4) If all else fails, just go at it alone. Don't waste the trip, find something to do(there's ton of things), you traveled that far, do something.