Lars is correct that Kewpie mayo uses only egg yolks and not whole eggs but the vinegar is wrong. Kewpie uses a blend of apple cider and malt vinegar. The proportions are secret so you'll have to experiment until you get it right.
Great taste, and so easy! I'm looking forward to trying this with steamed artichoke.
This was excellent, but you must run your food processor at full speed! I had to empty my processor, whip up another egg (with 1/4 tsp dry mustard) and then re-add the first attempt. It turned out perfectly the second time! I mixed a small portion with Sriracha to make dynamite sauce for sushi. Thank you!
Hint: Kewpie uses only egg yolk and not whole eggs. Also, msg (if you're not sensitive) will give you a more authentic taste. MSG gives foods an umami taste (the fifth taste... sweet, sour, bitter, salty, and umami). The rice vinegar is spot on...