Japan's culture is one forged in various degrees of shame. And that's a damn shame sometimes because it makes getting a quick STD test at your local clinic all the more socially cumbersome and logistically inconvenient. In my home country an AIDS/HIV test was usually "thrown in" with a yearly physical. I didn't even have to explicitly request it. STD testing is so commonplace in the USA that any shame associated with it has long since yielded to pragmatism. Unfortunately for Japan, STD testing still carries a lumbering stigma. I'll never forget the first (and only) time I requested one at my local clinic. The nurse abruptly broke eye contact, lowered her voice, and darted away to fetch a doctor. It was a tad awkward. The clinic a former employer used for their yearly health exams offered STD tests as an option, but lamentably I think that's comparatively rare as my current company's clinic of choice does not. And after my shame-inducing experience when directly requesting one, I hesitated to repeat that approach. An Internet search revealed some Tokyo clinics specializing in STD testing, but by happy chance I found some even more felicitous solutions to getting an STD test in Japan.
SOLUTION 1: Get a Home Mail-In STD Test
I found numerous home STD tests available on Amazon Japan, the most popular of which appear to be these:
1) This one tests for HIV (AIDS). It's a unisex test.
2) This one tests for five diseases: chlamydia, gonorrhea, hepatitis B, HIV (AIDS), and syphilis. It comes in a men's version and a women's version.
* Men's version: http://amzn.to/2t8Gqc7
* Women's version: http://amzn.to/2t4iyW8
Here's the whole "STD Checker" portfolio: Amazon Japan - STD Checker
The kits by "CellSeeFit" are also good, particularly for testing for multiple diseases at once. The 6-disease testing kit is quite popular and a pretty good deal.
* Men's version: http://amzn.to/2s96zlQ
* Women's version: http://amzn.to/2s9ict3
Here's the whole "CellSeeFit" portfolio: Amazon Japan - CellSeeFit
Instructions are included, but they're in Japanese of course. Luckily, the Japanese use manga for everything (including STD test instructions), so the pictures make it relatively easy to follow. Basically, you need to supply blood and urine using the contents of the kit.
* The urine test is simple--capture urine mid-stream using the included cup, then pour it into the tube. Cap it and label it. Easy-peesy. (Get it?)
* The blood test is a bit more challenging. Prick your finger using the included tool; then allow blood to evenly saturate at least 3 of the 4 cardboard sticks. Label the blood test packet.
* Fill out the one-page form, choosing a user ID number and a numerical password. It also asks for the date you took the test, but does not ask for any personally-identifying information (besides birthday) because the test is designed to be as anonymous as possible.
* The form makes a copy. Keep the copy for yourself because you'll need this info to login to the website to check your results.
* Put everything into the included pre-paid envelope and mail it.
* Several days later login to the website noted on the form to check your results.
SOLUTION 2: Get an Instant At-Home HIV Test
Amazon USA sells at-home HIV tests that don't have to be mailed in. Similar to an at-home pregnancy test, the results appear in 20 minutes or so. Doubly cool is that they use saliva instead of blood. Sadly, I could not find these for sale in Japan; however, you may have luck getting them shipped from overseas.
Oraquick seems to be a popular choice: Amazon - Oraquick Home HIV Test
The trick is finding an Amazon seller that will ship overseas.
* Under the "Other Sellers on Amazon" section, click the "X new from..." link. A list of all Amazon sellers selling the item will appear.
* Scroll through the list, paying close attention to the "delivery" section. Those offering international shipping will naturally have the word "international" in their delivery / shipping information.
The bummer about this approach is that the shipping cost may exceed the price of the product. Perhaps you could save some money by ordering several at once. Then you could give home HIV tests out to your friends on Christmas. Awkward! Best of luck to you, fellow foreigner!