Otaru Dining, which handles "low-carbohydrate diets," sells "low-carbohydrate fondant chocolate" for Valentine's Day only. You can purchase it from the company's mail order site.

How about fondant au chocolat with no sugar?
How about fondant au chocolat with no sugar?

This product uses soybean flour instead of wheat flour, and is a sweet that uses no sugar and reduces the amount of sugar to 5.9g (0.32oz) per piece. It seems that it has achieved 61.4% off sugar than usual. The slightly bitter and moist dough contains rich and mellow chocolate, and if you heat it a little in the microwave, you can enjoy the melty chocolate.

The price is 1,480 yen including tax (4 pieces, shipping fee not included), freezing delivery. Scheduled to be sold until February 14th.