Edit October 6: FALSE ALARM. I screwed up like I do everything else I do, maintenance is for the SQ Shop only. So you can still play the game, but can't (or advised not to) buy SQ during the "maintenance".
I'm really sorry for the wrong info.
Remember the post about changes to Saint Quartz packages coming into effect after October 5?
On October 6, 2022, JP server will have a maintenance from 0:00 ~ 12:00 JST to update the stores.
It's been quite a while since we have such a long maintenance, so don't be surprised if you can't login.
https://news.fate-go.jp/2022/1006uwhc/