I've been to Mitsuwa in San Jose and Irvine as well, and each location isn't just a supermarket; it's more of a one-block Japan Town, with a Sanseido bookstore, Shiseido shop, and food court.
The food court
Mitsuwa is most famous for Santouka ramen, which I eat every time I come here. I got the spicy miso ramen with pork cheek and an ikura-don (salmon roe over rice) for $16--it's pricy, but it would be a lot more expensive in Manhattan.
After lunch, I got an obanyaki with cream filling. The cream was light and not too milky--just the way I like it--but the outside crust(?) was soft and had a plasticky texture. It also had this weird savory quality to it; I can't quite place my finger on it, but it tasted like kombu broth.
I love the supermarket for the Japanese snacks. Although they're not much cheaper than other Asian marts in Manhattan (M2M, Sunrise Mart), Mitsuwa has a much larger selection, and it just feels cleaner buying stuff from here than from dingy little East Village and Chinatown shops. (Have you ever visited Hong Kong Supermarket? You know what I mean).
The supermarket also has an amazing selection of beauty and household products. The beauty products here are actually a bit more expensive than stores in Chinatown ($19 for a bottle of Oshima Tsubaki oil vs. $16), but you come here for the variety.
The produce here is so beautiful and fresh and cheap!
Perfect, unblemished potatoes and cabbage!
The bookstore
Sanseido sells Japanese books and magazines exclusively, so it isn't much fun for me to shop in; the only English books are the likes of The Art of Zen. The stationary section is quite limited (and expensive for the quality) too--you're better off shopping at Muji for your Japanese pens and diaries.
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Mitsuwa is great if you want to get out of the city for some good ramen and to stock up on Asian snacks. The shuttle is $3.00 each way (except Wednesdays and Thursdays, when shuttle service is free from Manhattan!) and takes about 30 minutes from Port Authority. If you can, try to go during the weekday; on weekends the food court is super packed!
Mitsuwa
http://mitsuwa.com/
Hours: Everyday 9:30am to 9:00pm, restaurants 11:00am to 8:00pm
*Free shuttle service on Wednesday and Thursday!*