The product is called Petit Mont Blanc...it's a chocolate-like treat made with chestnut filling. The concept plays with the idea that chestnuts ("kuri" in Japanese, which Ayu repeats over & over again in the CM, hehe) look similar to sea urchins ("uni").
Hope that helps.
I too love that CM...(there are actually two, I believe...one of them with her at a sushi restaurant & then another one with her in a park??)