The operator of a major conveyer belt sushi chain that became the center of national attention over a viral video of a boy licking a soy sauce bottle filed a 67 million yen ($480,000) damages suit against the boy, court documents showed Thursday.

Akindo Sushiro Co., which runs the Sushiro restaurant chain, filed the suit at the Osaka District Court on March 22.

According to the complaint, the boy went to a Sushiro outlet in Gifu Prefecture with a friend on Jan. 3 and was filmed licking an open soy sauce bottle and an unused teacup, and then touching a passing plate of sushi with a finger covered in his saliva.

The video was uploaded on social media by Jan. 29, and Sushiro restaurants saw a sharp fall in customers after it was shared widely.

Supplied photo shows a variety of sushi at sushi restaurant chain Sushiro. (Kyodo)

The suit also claims the footage caused its parent company's market capitalization to fall by more than 16 billion yen from Jan. 30 to 31.

Akindo Sushiro is installing plastic barriers at over 600 outlets nationwide among other measures, resulting in a loss of 90 million yen. The sushi chain operator could seek higher damages reflecting these measures.

The 45-second viral video caused a stir in Japan and helped give rise to the term "sushi terrorism" to describe unhygienic behavior in the restaurants.

Food is typically served there on plates that pass numerous diners and utensils are set at the tables ready for a succession of customers to use throughout the day.

The boy has admitted to licking communal items and expressed remorse. But his defense team argues that the footage was for sharing only among his friends, and that he had no intention of creating a video to be spread online.

They claim there is no clear causal relationship between his actions and the fall in customers due to stiff competition among rival sushi chains, according to the documents.

Akindo Sushiro declined to comment on the matter.

Sushiro's competitors, including Kura Sushi Inc., were affected by similar scandals earlier in the year, with a man in Nagoya, Aichi Prefecture, indicted for obstruction of business for licking a soy sauce bottle top at one of its restaurants.

Outside the sushi business, a man in his 30s has also been indicted on the same charge after he was filmed eating red pickled ginger straight from a communal bowl at a branch of a Yoshinoya Co. beef bowl chain restaurant in Osaka.

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