This candy called to me; the packaging was so cute that I had to buy it. It's a Japanese explosion with the cherry blossoms, daruma, ume (Japanese plum) flavor, and the fact that it's marketed have the effect of helping students pass their exams.
The package also advertises "sour powder" inside the chew, which makes sense, as ume (especially umeboshi, or pickled plums) are incredibly sour. Umeboshi tend to bring out strong feelings in people, in that they either hate them or love them. The high citric acid content not only results in a sour taste, but some possible health benefits.
As for the candy, it smelled really sour and a little salty, like umeboshi. The outside was a bit sweet and a little plummy, but as I chewed, it got very sour, salty, and juicy. It was so sour that I really was reminded of the real thing, down to the hint of bitterness. It made my eyes water just a little bit.
The innards seemed slightly softer than a regular Hi-chew, and you can see in the picture that the inside is a bit spongy. The sour punch was really surprising, and I think this would be great for plum fans. It wasn't as intense as umeboshi can be, but it's candy, so that's just fine with me.
Morinaga Website (Japanese)