The wonders of MSG-laden Kewpie mayonnaise are a fairly recent discovery for a lot of chefs in North America, who have embraced its strangely adorable packaging and intense umami by putting it in everything from late-night mortadella sandwiches to softshell crab sliders to ranch dressing. But the undisputed king of mayo goes back almost a century in Japan, where, far from relenting, Kewpiemania is only ramping up. Today is officially National Mayonnaise Day in Japan, and in keeping with a recent tradition of mayo-based pop-ups, Kewpie is flexing its umami muscle and will be setting up shop in two separate storefronts to offer a mayo-centric menu. According to Kewpie’s website, “Kewpie Mayo Cafés” will be opening in Tokyo’s bustling Shibuya district[…]