Preheat oven to 350°F. Grease two 4-inch round pans. Whisk flour, cocoa, baking powder, baking soda, and salt. Mix milk and coffee.

Beat 1/4 cup butter and sugar until fluffy. Add egg and 1 tsp vanilla. Alternate adding dry ingredients and milk mixture. Divide into pans and bake 20 to 22 minutes. Cool completely.

Beat 1/2 cup butter, powdered sugar, and 1 tsp vanilla with milk to make buttercream. Tint portions orange and green, leave remainder white.

Level cakes and trim to rectangles. Stack with white buttercream, crumb coat, and chill 20 minutes.

Pipe white buttercream on top in short squiggles, then drag a fork to make rice texture. Smooth sides with white buttercream. Chill while making decorations.

Knead and color marzipan. Mold a duck body, head, beak, feet, and tiny green vegetables.

Cut nori into a strip, press onto one side of the cake. Spoon green buttercream behind it, place vegetables. Set duck on the rice bed. Serve chilled.