One of the videos, taken at a Sushiro outlet, shows a diner who appears to be in his teens licking the spout of a communal soy sauce bottle. He then licks the rim of a teacup and puts it back on the shelf. As the clip went viral -- racking up tens of millions of views -- it caused stocks in the restaurant's parent company, Food & Life Companies, to slump.
The firm responded by filing a report to police alleging reputational damage.
"We take this matter very seriously because it undermines the trust between the operator and its customers," Food & Life Companies said in a statement. "Our customers have been disgusted by this video, which is completely unacceptable."
The company said that although the teen in the video and his parents have both apologized, it intends to pursue the matter as both a criminal and civil case.
Twitter users reacted to the incident with fury, describing the video as "sickening." Some said they would think twice about eating at a sushi restaurant again.
The company has also taken countermeasures to prevent similar incidents. Customers at the affected restaurant and at nearby outlets must now bring utensils and condiments to their tables from a central service point. The company says it will also provide freshly disinfected tableware at the request of diners at any of its locations nationwide.
More prank videos
In footage filmed at the sushi chain Hamazushi, a customer puts wasabi on someone else's order as it passes him on the conveyor belt.
And in yet another prank shared on social media, a diner at an outlet of the noodle restaurant chain Sukesan Udon eats spoonfuls of tempura toppings with a communal serving spoon. The operator says it has also filed a report to police.
A series of prank videos taken at karaoke chain Karaoke Manekineko also recently appeared on social media. One clip shows a man pouring soft serve ice cream from a self-service machine directly into his mouth. The company says it has disinfected the ice cream machines at all 600 of its stores nationwide.
Social media to the rescue
The initial social media backlash has given way to an outpouring of support, with many people posting images or videos of their visits to Sushiro outlets with the accompanying hashtag #saveSushiro.
The company's president, Nii Kohei, wrote on Twitter that he felt overwhelmed by the kind words: "I'm so grateful I could cry."