The country’s ubiquitous convenience stores throw out huge amounts of edible food. In Tokyo, Rachel Nuwer meets the campaigners trying to change that.

Riko Morinaga, a recent high school graduate in Tokyo, normally spends her weekend nights hanging with friends. But 3 February was different. That Saturday night was Setsuban, a Japanese holiday celebrating the transition into spring. It also happens to be one of Japan’s biggest food waste days.

Every year on Setsuban, stores across the country stock a holiday sushi roll called ehomaki. At the end of the night, hundreds of thousands of these rolls wind up in the garbage. “Shops always provide what customers want, which means their shelves have to always be stocked,” Morinaga says. “This contributes to the food loss problem.”

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Based on the data Morinaga and others gathered, Rumi Ide, an independent researcher, activist and journalist who coordinated the survey, extrapolated that Japan’s 55,657 convenience stores threw out 947,121 ehomaki rolls worth 700-800m yen ($4.5-5m; £3.6-4.1m). Ide published these results on the news website Yahoo Japan (unavailable in UK and Europe) to raise awareness about this hidden problem.