Captain Wataru Endo warned that Japan's Asian Cup rivals will "exploit" its weaknesses after it wobbled before reaching the quarterfinals with a 3-1 win over Bahrain on Wednesday.
The four-time champions will play either Iran or Syria after a last-16 victory in Doha that saw Brighton winger Kaoru Mitoma return from injury.
Japan looked to be cruising after goals either side of halftime from Ritsu Doan and Takefusa Kubo, but an own goal from error-prone goalkeeper Zion Suzuki let Bahrain back in the game.