score:13
While Japanese citizens under 20 years of age are considered minors, Japan is a signatory to the Hague Convention on the Civil Aspects of International Child Abduction, and its Ministry of Foreign Affairs has a brochure, in English, which should respond to your concerns (added emphasis mine).
- A consent letter for travel from the other parent is required in some countries when you enter/ depart the country. A permission from the court to leave the country with your children is required in some countries before leaving.
- A consent letter is not required when leaving / entering / departing Japan.
In what cases, does the Convention apply?
- If they are under the age of 16, the Convention will apply
So, as a US citizen, she may enter Japan visa free; as a 17-year old, under the Hague Convention, she is not considered a minor when travelling; and Japan does not require parental consent for her to enter the country. It would be a good idea for her to have her parents' accommodation details, to know whether they are reachable on their mobile and, surely, they'll be at the airport awaiting her arrival should there be any hiccups.
As an observation, every year, many US teens travel independently to Japan for high school exchange programs, entering both visa free and on student visas.
Upvote:6
From personal experience: I doubt the immigration officer will raise an eyebrow, especially if you don't speak Japanese.
I visited Japan the first time when I was 16. I traveled with my friends, but did not meet up with them until I passed immigration. At the time, I didn't speak much Japanese, so I showed the immigration officer my passport and he asked me how many days I'd stay. I said I'm staying for 10 days, and they just stamped my passport and let me in. No questions asked.
In fact, I believe the immigration officers see this quite often, as Japan is very popular with young people and many teenagers do travel to Japan alone. Their only problem might be at the airline check-in counter, because some airlines do not allow minors to fly alone, or might have them sign extra paperwork. Be careful about that!
If you do answer them in Japanese, though, they typically will be a bit more interrogative, but just a few questions and you'd likely still be let in.