Jia Jin Low
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Possibly the best bean-stuffed warabi mochi in Japan. Some have argued that you can get 80% of the way there with a good stall in a depachika, so why bother coming all the way here? And in a way, they’d be right. But if you seek perfection, then make the trek out here, and order one more warabi mochi than you think you need.
They also do pretty good renditions of other wagashi, but those are just 4/5 for me.
Also, they close pretty irregularly, so if you’re short on time, call before coming down. Out of the 4 times I’ve been, it was closed once on a non-store-holiday.