How to get Citizen ship

Goingn to live & work in Japan is a great goal to have. I've been twice with my J-wife and I love it. Just study hard, learn fluent Japanese and work on your visa's. I also recommend that while in college, you go over for a year under a student exchange program. My sister did this in college and it was a great experience for her.
s far as citzenship goes, though, think long & hard before you consider giving up your US citzenship. Once you do so, it will be very hard to get it back and will make it extremely complicated to return to the US permanently if things don't work out in Japan. You will have to apply for visas & green cards just like anyone else looking to imigrate to the US.

cf are you sure? I know to get citizen ship in japan you have to give it up in another country but as long as you have an american birth certificate your a US citizen I know some otehr countrys my be a pain about it but I dont think you can ever truely give up your US citizenship.

You can give up US citzenship. And under certain circumstances, you can forfeit it, for examply by serving in the military of another country. This is clearly stated in US passports.
Also, the US & Japan do not mutually recognize dual citzenship. So, in order to gain Japanese citizenship, he may need to give up his US citizenship, especially since he has no family or historic ties or other claims to Japanese citizenship.
In either case, any US citizen looking into getting citizenship in another coutry needs to contact the US State Dept. and make sure they fully understand the implications. Its a big step and and you need make a more informed decision than simply getting advice from an internet forum.