I was surprised to see that Sweden transferred its remaining plutonium to the United States around a decade ago. I would have assumed they’d have kept it around, just to keep their options open - it’s not like they were in an immediate post-USSR situation where unpaid nuclear scientists and unsecured cores were potentially up for sale and there’s a strong international interest in shutting that down. But then again, if Sweden did keep their options open, it’s not exactly the kind of thing they’d advertise - and the public story of the plutonium transfer is useful plausible deniability.

Japan, obviously, for a variety of reasons, doesn’t have nukes, but it seems pretty clear they could have an arsenal that’s functional as a deterrent in months, if not weeks. I wouldn’t be surprised if Sweden’s current doctrine is similar to that (though now being a formal member of NATO takes some pressure off that backup option).