Passersby walk on the street at Shibuya shopping and amusement district in Tokyo, Japan, July 28, 2022. Photo by Reuters
The students were rushed to hospital after the stabbing at the McDonald's in the city of Kitakyushu, in Fukuoka prefecture, the Jiji news agency said.
The female student died, while the other victim, a boy, was conscious, it added.
A male suspect fled the scene at around 8:30 pm (1130 GMT) and police were searching for him, according to Jiji.
The suspect is believed to be armed with a knife, it said, citing police.
Violent crime is rare in Japan, which has strict gun control laws. But there are occasional stabbings and even shootings, including the assassination of former prime minister Shinzo Abe in 2022.
In 2019, two people including a schoolgirl were stabbed to death and more than a dozen wounded in the Japanese city of Kawasaki in a rampage by an attacker who targeted children as they waited for a bus.
The 51-year-old attacker slashed at a group of children before fatally stabbing himself in the neck.