The Japanese movie Sweet Bean (あん) shows the process of making red bean paste in one of the scenes. The cook uses a clear gelatinous substance which presumably is the sweetener for this paste. What is it exactly?
The ingredient is Mizuame (水飴), a Japanese sweetener. It adds sweetness and gives a luster.
When they need large amount, professional cooks usually scoops it with their bare hands, as she does in the movie. I'm not sure of the reason, but Mizuame is very sticky and it is troublesome to handle with tools.
And this behavior explains that she has long experiences in making read bean paste.
I've not seen the movie but from my knowledge and the recipes I just reviewed, bean paste is typically sweetened with regular granulated sugar. Could the gelatinous substance maybe be a thick simple syrup of water and sugar?
I tried to find clips from that specific scene online and didn't have any luck.
There are also candies that use red bean paste as an ingredient that include gelatin.
I would assume that it is Agar, a seaweed gelatin common to Asia. Agar, unlike gelatin made from animals, can remain in a gelatin form at various temperatures, so it's likely they had gelatinized it, then were re-liquefying it into the mixture in order to gelatinize it again later.