I really haven't been staying on top of the Japanese food scene much. It didn't actually seem like there was a whole lot going on anyway, although I've known for some time that Santouka Ramen was coming to Harvard Square. Eater seems to be on top of it though so if you want news, check here. They are reporting a February 11th opening. One of my friends wanted to know if I'd be first in line but frankly it's too damn cold this winter!
I heard tonight that Beard Papa's (Wikipedia), a Japanese cream puff chain, is returning to Boston! I went to their Faneuil Hall location once years ago and it seems they used to have a store in the North End as well but they'll be located in Chinatown this time. You can get updates on their Facebook page. Word in the Japanese community is that they will open in February.
Then there's Kyoto-based Japanese coffee chain, Ogawa Coffee. I hadn't heard of it, but apparently it's a big deal. See the Globe's: Ogawa Coffee planning to make US debut in Boston which reports they will open in Downtown Crossing. The Globe says they'll be the first Japanese coffee chain to open in the US and their reasoning for opening in Boston over New York City is interesting. One reason being that Boston and Kyoto are sister cities. No rumors of an opening date yet.