Here's the deal, the process is in flux basically. A few months ago I could go straight home and would have to quarantine there for 14 days. It seems a lot of foreigners were breaking the quarantine though and that may be why the gov. changed it to a hotel stay instead. As it stands right now only Japanese nationals and permanent residents are allowed in the country. You will be taken by the government to a quarantine hotel for 7 days, which includes the day you land in Japan, but officially the first day does not count, so they say you have to quarantine in the hotel for 6 days. You have to take 2 covid tests in the hotel on the 3rd & 6th day. If you are negative you will be taken back to the airport and must be picked up by someone to be taken home where you have to quarantine for 1 more day.

I imagine by the time you come for your cousin's wedding the restrictions will be completely dropped, unless of course they keep shoving needles into people's arms and giving them COVID mutations.

You can follow the Gov. policies on the MHLW site https://www.mhlw.go.jp/stf/covid-19/bordercontrol.html