Ingredients: Water, granulated sugar, sugared chestnut, red bean, trehalose, agar-agar, salt, colour (gardenia), sulfite
The taste was ... well, ok. I had eaten better chestnut and red bean based sweets in Japan. It was not really bad though, but not exciting either. The centre was a sugared chestnut with a sort of rough red bean mash engulfing the chestnut.
But now to the 'natural ingredients'. I guess you could call sulphites 'natural', and it is most certainly used to keep the chestnut from discolouring. On the other hand sulphites do pose health risks. Sulphite sensitive people and people suffering from Asthma, are prone to reactions similar the one caused by food allergies. Is it really unavoidable? No, ascorbic acid would have done the trick and with no ill effects.
The second point is trehalose. Why on earth did they put this novelty sugar in it? This time we can't speak of a natural ingredient. Although some fungi, insects, and bacteria do possess natural trehalose, the one put in our food is not: "Hayashibara started manufacturing trehalose by activating two enzymes, the glucosyltrehalose-producing enzyme that changes the reducing terminal of starch into a trehalose structure, and the trehalose free enzyme that detaches this trehalose structure. As a result, a high-purity trehalose from starch can be mass produced for a very low price." (Wikipedia). The product trehalose seems to be safe from a health aspect, altough it is not even yet known how many people do indeed possess helase, the enzyme to split the double sugar and digest it - after all we are neither fungi nor insects. There may very well be the same risk of intolerance as when adding lactose to food products. Furthermore the two main enzymes "were not evaluated completely to JECFA standards for general food safety. The Committee VNV agrees with the first assessor that the applicant should be strongly encouraged to submit the enzyme preparations for formal evaluation." Meaning there is still enough uncertantity about this novel food.
Do we need it for a good (or in this case mediocre) wagashi? Definitely not!
If you want to go for your own version (and I cannot encourage you enough), there is a chocolaty version on E-recipe and a kind of 'deconstructed' version on cookpad.com.