Not that you will lack of things to do if you are in Japan but if you love the place so much and are running out of some fun ideas I suggest that you go on a Bear Watching Trip just outside Tokyo.
Bear watching trips are run in association with the Shinshu Bear Research Organisation. The guide, Oscar Huyens, is known for being first person in Japan to obtain a PHD from studying Asiatic black bears, hence ensuring that you not only get to catch a glimpse of the wonderful bers but that you willl also get an earful of knowledge.
The tour isn’t for lazy people since you will need to go to the town of Matsumoto and from there travel into the mountains by car before hiking on foot to go to the mountain lodge to stay overnight and hike back down the valley in the morning while being led by the tour guide. If the visitor doesn’t see a bear during the tour the person gets his money back.