For decades after the 1989 crash they were in deflation. Only in the last 3-4 years has any meaningful inflation returned. Some context here: https://en.wikipedia.org/wiki/Lost_Decades
For like past 30 years yes. The inflation during that time were covered by shrinkflation and value adds through feature adds. I think some argue it has to do with lack of popularity of credit cards and electronic payments, which nudge prices to gravitate towards nearest coin denominations which in turn suppress inflation. Which is probably true, considering if a bottle of soda went from a dollar and a dime to a dollar and two dimes, or the umaibo went from one dime to a dime and three cents totaling as four distinct coins, those will be very tangible to consumers.
Historically, no. Prices were basically flat for a long time until covid.
They've also been making things smaller. Some would argue that it's a cultural thing, but being poor also means you have to start adopting austere cultural habits as a coping mechanism.
There's shrinkflation for sure. Take Torikizoku for example. One plate = 280yen from 1985 until 2017. Now it's risen to 337yen while also reducing in size by 30%.
Population is flat or declining so that's one of the main drivers of inflation. Japan could be a pioneer in steady-state economics.
Over the long run, population decline it is associated with disinflation or deflation. Deflationary forces often become strong because overall demand and economic growth slow.