One of the best ways to entertain guests in Japan would be to give them the opportunity to ride the shinkansen (bullet train), show them Mount Fujii and, if possible, allow them to take part in a live tea ceremony. Maybe even give them a chance to see Akihabara, the famous electronics district.
If time allows, I also recommend taking them to places where they can interact with things, like the Iga Ninja museum, where they can take photos with old ninjas, or even learn how to throw ninja stars.
You could also give them the chance to dress up as a Maiko or even a samurai, then take photos of them, so they can have a good laugh when they show their friends at work.
I had a best friend who came here. Nice guy, Caucasian guy, New Yoaka, culinary specialist. However, even with all of his culinary knowledge, he was unable to fully appreciate the Japanese palate.
So this is the official way you would entertain guests if you absolutely had to:
1) Food, food, food. Nothing exotic. Start with recognizable Japanese favorites like tempura and yakiniku, that way they won’t crave something heavier later. If their diet changes too soon, coupled with jet lag, they will enjoy their trip less. Sometimes McDonald’s is fine for lunch.
2) Do not rely on public transport to get around Rent a car. Choose easy routes. Just get on the Kanetsu expressway and get on to Niigata. Show them the backcountry or maybe even Gunma. Lose yourself a bit.
3) Do not do onsen unless it is a mixed bath. Take them to Yunneson in Hakone instead, that way they can spend time walking around in swimsuits with you. Remember to try akasuri, which in English is called skin peeling. Japan will be the cheapest and most accessible place to do it. Everyone has to try akasuri at least once while here! It is a must. I get it twice a year.
4) Take them driving driving driving. Sometimes people can become much more immersed in their surroundings when in a car than on foot. Sometimes you don’t have to talk about the experience. Let them feel the country for themselves.
5) It is better to visit the shrines because they are less crowded. Show them how to wash their hands and teach them a bit about the history of the shrines. Kamakura is the perfect place for this.
Remember, never forget wagashi, or Japanese sweets. It is essential that they feel and appreciate a good wagashi. Go somewhere expensive, not somewhere cheap.
Finally, and this is a big one. Remember to take your guest to an authentic or red lantern restaurant, which is a place where working class people can drink cheaply.
The reason is that they need to experience the real side of working-class Japanese every day, and what it means to eat normal food.
That is all!