Koyadofu, I suppose. It's tofu that's been freeze-dried and rehydrated, which gives it a spongy texture. If you've ever had a McGriddle, imagine one of the mini-pancakes from that, without the syrup bits, and totally saturated with water. It's remarkably similar to that.
Sounds disgusting, but it's actually rather nice if you squeeze out most of the water and dip it in soy sauce. And I don't even like tofu that much.