The sushi style that uses a strip of nori around rice to hold loose toppings like roe is gunkan-maki.
The name means “battleship roll,” referring to the raised band of nori that surrounds a compact bed of vinegared rice. Unlike a conventional maki roll, the seaweed forms a small open-sided cup, making it practical for toppings that are too loose, soft, or wet to sit neatly on ordinary nigiri.
Gunkan-maki is especially associated with ingredients such as ikura (salmon roe), tobiko (flying-fish roe), and uni (sea-urchin gonads). The style is widely credited to Ginza’s Kyubey restaurant in Tokyo, where it was developed around 1941. The innovation solved a practical sushi problem: delicate toppings could be served without being pressed into the rice or falling away.
It is often confused with hosomaki, which is a thin rolled sushi, or uramaki, an inside-out roll with rice on the outside. Oshizushi is different again: it is pressed in a mold rather than shaped by wrapping rice with nori.