A perennial favorite is umeboshi, or salted plum. Or perhaps mentaiko, which is hot, spicy roe. But in principle, anything can be placed inside onigiri, even sausages or cheese. Then the ball is ...

Must-try dish: Don’t miss the Fukuoka-style mackerel fried rice, satisfyingly salty and complex with shredded grilled mackerel, shiso, and umeboshi ... the rest home as onigiri.