https://www.ph.emb-japan.go.jp/itpr_ja/00_001000.html
Q17: Are there any restrictions on the number of times I can enter Japan?
A17: There is no limit to the number of times you can enter Japan. However,, if you intend to stay in Japan for more than half of year (180 days) as “Temporary Visitor”, you might not be allowed to enter Japan since it may not be regarded as temporary visit.