Almost all houses in Japan are bought along with the land. Occasionally there are leasehold properties. I have seen 50 year residential leaseholds owned by a temple, but they are rare.

Sounds like the have a mix https://resources.realestate.co.jp/buy/leasehold-rights-in-j...

Typically people own both, although there are cases of people building on leased land.

The land value is assessed separately from any structures built on it for the purposes of taxation, which I think is what they mean when they say it is “calculated separately”.

That's how it's done in BC Canada.

Most people for houses own the land and building.

These are assessed separetly for taxation purposes/assessment value.

Some areas are leased land for say 75 year contracts or any other long term (alot of indigenous/native owned land that is leased for a term contract. There's some condo development and mall with a 100yr lease etc)

I haven't seen many leasehold properties, but I did come across one area where a bunch of vacation homes are built on property that is leased by the government.

Here's one I found that actually looks looks pretty nice for ¥3M (USD $21K). But the lease payments and administration fees probably scare away any prospective buyers (it's also in a forrest in one of the snowiest areas of Japan, so accessibility in winter might be a bit of an issue).

https://www.yuzawacorp.jp/detail/dtl.html?no=18094507

Note that this one mentions 借地料, meaning that you are not an owner of the land, but the government is lending it to you for a yearly fee of 220,000 yens.