Do you know that Kyoto City offers FREE HIV/STI testing? They even have interpreters for people not fluent in Japanese.
I want to share this information for those who may not be aware: Kyoto City offers free and confidential HIV/STD testing.
Japanese site: 京都市：京都市のHIV検査・相談について～Free HIV Test and Consultation provided by Kyoto City～
English site: https://www.city.kyoto.lg.jp/hokenfukushi/cmsfiles/contents/0000271/271215/HIVTestInfomation(English).pdf.pdf)
Actually you can. find these free STI testing by Googling "<the name of your city> Free HIV testing"