This is a policy statement: https://www.jarl.org/English/3_Application/A-3.htm
This is a description provided by Taiyo: https://www.hellocq.net/forum/read.php?tid=370371
I followed this guide and, after about 40 days, received the exemption certificate from JARL. I also obtained a callsign for JS2. For Chinese HAMs, the prerequisite is to have either an FCC license or a similar CEPT license.
This Japanese temporary license is actually quite useless. The validity period I was granted is only 90 days (apparently, it used to be one year). Renewing the license requires payment and is done through manual email interaction. Therefore, it may only be suitable for a simple experience while traveling, but not for non-permanent residents who want to maintain a Japanese radio license long-term. However, isn't amateur radio all about trying out new things and experimenting? Experiencing this process does have some value.