Will he stay or go? For Prime Minister Shigeru Ishiba, a number of key political events in the coming weeks are expected to affect the timing of any decision to quit or remain in his post.

Ishiba has reiterated his intention to stay in office — in defiance of growing calls for him to step down from within his Liberal Democratic Party after the party's poor showing in the Upper House election this month.

"I'll manage the nation with my utmost sense of urgency and responsibility to leave a better Japan for the next era," Ishiba said in a speech in the resort town of Karuizawa, Nagano Prefecture, on Friday.