It’s not actually Japanese, it’s a Russian cultivar, a member of the purple tomato family . It has a pinched top, and thus looks like a kind of pear. Don’t let the looks fool you, this thing has incredible flavor.
I’ve been lucky enough to have a coworker that grows these things. He tells me they don’t refrigerate well, you need to store them at room temp and eat them quickly. They don’t need much more than a little cracked pepper to deliver delicious flavors.
Notes: Interesting links to the trifele can be found on the Tomato Gardener, This Garden is Illegal, and Moonglow Gardens. Things from Scratch has a beautiful picture of growing plants. The blog Tomato Lover has more than one article on the trifele, of which this the article, “The Move Into Red”, has the best photograph. Austin Urban Gardens has a short blurb on how the trifeles taste.