Gather all the ingredients. You will need a Nagashikan (6” x 5.1” x 1.8” high (15 cm x 13 cm x 4.5 cm high)) or a similar-sized container lined with plastic wrap.
In a small saucepan, add 2 cups (480 ml) of water and 4 gram kanten powder. Whisk to combine and bring it to a boil.
Once boiling, lower the heat and cook for 2 minutes. Whisk occasionally and make sure kanten powder has completely dissolved. After 2 minutes, remove from the heat.
Add ¼ cup (4 Tbsp) sugar and whisk till sugar is completely dissolved.
Run water in the mold (or nagashikan) and pour the liquid until there is about ⅓ inch (8 mm) in the mold (so that fruits won't touch the bottom). Using a spoon or toothpick, move the bubbles on the liquid to the corner and remove them. Let cool in the refrigerator for just under 10 minutes or at room temperature for a little longer time.
Meanwhile cut fruits for the jelly.
The thickness of the fruits should be about the same.
When the bottom layer is slightly set (not liquid or completely set), place the fruits on top. If the bottom layer set too firm, the top layer will not attach to the bottom layer well and the fruit jelly will separate into the top and bottom layers when you cut. The liquid in the saucepan should not be solidified since the saucepan is still warm and it has more liquid in there. If solidify, then re-heat till it turns to liquid.
Then pour the rest of the mixture and pop/remove the bubbles. Keep in the fridge until the jelly has set completely.
Run a knife around the mold and gently flip and unmold the jelly. If you’re using the nagashikan, run a knife around the mold and pull up the handles.
Cut the jelly to around the fruits so they look prettier. Serve chilled on a plate.
You can keep the jelly in an airtight container and store in the refrigerator for up to 2 days.