In a mixing bowl, combine glutinous rice flour, sugar, vanilla extract, and a pinch of salt. Gradually add water while stirring to avoid lumps. Mix until the batter is smooth.
Pour the rice cake batter into a greased and lined square or round cake pan. Steam over medium heat for about 20-25 minutes or until the rice cake is set and a toothpick inserted comes out clean. Allow the rice cake to cool completely before cutting it into desired shapes.
In a blender, blend the diced kiwis until you have a smooth puree. In a saucepan, combine the kiwi puree, sugar, lemon juice, and water over medium heat. Bring the mixture to a simmer, stirring occasionally.
Sprinkle the agar-agar powder into the kiwi mixture, stirring continuously to avoid lumps. Continue to simmer for 5-7 minutes or until the agar-agar is completely dissolved.
Remove the kiwi mixture from heat and let it cool slightly. Pour the kiwi mixture over the cooled rice cake in the cake pan.
Place the cake pan in the refrigerator and let it chill for at least 2-3 hours or until the kiwi jelly is set. Once the kiwi jelly is set, cut the rice cake with kiwi jelly into squares or desired shapes.