Legalities of staying with someone?

Next month I was going to visit Osaka and stay at a friend's house while visiting. However, I am underage [17], and have not been able to find out for certain if this is legal. It is just with one other person, but I would have my parents' written permission. Is this illegal? Even with the permission? The last thing I want to do is cause any trouble for them because of a simple visit, or myself or family.
If you could also provide a site explaining this, and/or other legalities, it would be appreciated.

[Also, I am new here, so please excuse me if I did anything wrong concerning posting..]

The only thing you did wrong was to post to travel questions. Japan is not Stalinist Russia and I don't think it matters who you stay with as long as you are not engaging in any illegal activity whilst staying there.

Just as (I'm assuming) you don't need permission to stay at someone's house in your home country, you don't need legal permission here either.

I doubt anyone can point you to websites with information confirming this, because there are almost certainly no laws relating to this situation- Japan is a free country, and whether under 18 or over 18, Japanese or foreign, you can stay with whomever you want. This is not something you need to be concerned about.

Provided you do specify a place to stay (address necessary) on the arrival form that you hand to Immigration officials, they will be quite happy, and you are unlikely to deal with the authorities at any other point during your stay until you go through passport control at the airport again.