Mix soy milk, water, agar agar and sugar in a pot and bring the mixture to a boil. Do stir frequently.
Once everything is melted, pour into little containers/glasses and refrigerate till set.
Top with the longans before serving.
Notes
I used readymade soy milk with added sugar, thus I didnt have to add too much sugar to sweeten the jelly. If you are using sugarless soy milk, you would have to add more sugar.
Recipe by Maya Kitchenette at https://mayakitchenette.com/soy-milk-jelly/