Social insurance payments while on medical leave

A few months ago I was given a diagnosis to take off from work for six months, and accepted it. It has indeed been great for my mental health to not have to go in to work every day.

But I've got some questions, and since the people who would normally answer that (company HR) are the very people who caused me so much stress, I'm looking for some outside advice.

I had the maximum 40 days of PTO available, so for all of August and September I was paid normally, and taxes were withheld normally. This month I'll have 欠勤 kekkin, which just means absence but implies that it's unpaid, status, and next month I'll have 傷病休 (not sure of the word; still a part of the company, but on unpaid medical leave).

Normally someone would be eligible to apply for 傷病手当 assistance starting next month, but I have a bit of side income (60k/mo, 資格外 permission granted; full time base pay had been 320k), which makes me ineligible for any assistance at all. I'll be living off savings until January. But I have no idea how social insurance payments work in this situation.

I know that kōsei nenkin (employee pension) is set for the entire next 12 months based on what you earned in April, May, and June. So I'm stuck paying about 30k yen per month even when I have no full time income?

Also, health insurance. That's a percentage of what I earned, but how about now, when I only have a small part-time income? My part-time job isn't taking anything out for that. Should I be going to city hall to sign up for 国民健康保険?

I realize that I should know these things, having been in the country for over 20 years. But I've been fortunate to never have any break or irregularity in employment. And I know that the government is getting very strict with even the most minor infractions by immigrants with this stuff.

What do people in this situation do? I know that the pension premium is already set, and ideally I would only pay insurance as a percentage of my new "income", but I'm prepared to accept whatever the system requires. I gratefully appreciate advice from anyone who's been in the same situation.

by ExhaustedKaishain