A bit over a year since y'all escalated this to the Community Team — apologies for the delay there! But the good news is you now officially only need 3 close votes to close a question on Japanese Language SE!
After looking at the data, I think it's clear that there's no reason for y'all to have this set at 5. Thank you so much for bearing with us while we got to this request.
We'll check back in with you all in a few months to see how things are going — if things are going great, we may not post an update but please feel free to leave a comment if you want us to post something.
Here's some basic stats of how things look:
Over the last two years, you've had decent numbers when looking into what percentage of questions that received at least one flag or vote to close actually ended up getting closed. While there are some dips here and there (the one in early 2022 is particularly noticeable), things have been generally in the 60-90% range and, the numbers of posts this represents are relatively small.

Additionally, the graph below shows that the community is doing the bulk of the closing — which is a good thing!

When working on this project, Catija had found two primary use cases for this change:
- When too many items are going unhandled (not unclosed, just unhandled)
- When the moderators are doing the bulk of the closing/reopening.
The second point there is moot, given the fact that the community appears to be doing about twice as much closing as the mods. But the first graph still shows that there's around ~20% of tasks aging out from the review queue on any given month. The hope is that changing this to three votes to close/reopen will make it so that first graph grows closer to 100%!