[sarasi]

The unofficial limit seems to be 180 days in Japan in a 12-month period. I know a lot of people who have been given a second tourist permit after a short trip to Korea or Taiwan, but the third permit in a row seems to be rare to non-existent. Even when coming back in the first time you can expect to be questioned, although if you are from a developed country it seems they will usually let you back in.

If you can stick to the 180 days in a year limit (and convince Immigration that you are not working here), then you should probably be ok.