Preheat the oven to 170°C (338°F).
Add eggs and sugar to a bowl and whisk together.
Add melted butter and milk, and mix well.
Sift cake flour, baking powder, and salt into the mixture and combine.
Divide the batter into two portions; mix green tea powder into one portion and melted dark chocolate into the other.
Alternately pour the green tea and chocolate batters into a pound cake pan, then swirl with a toothpick for a marbled effect.
Bake in a 170°C (338°F) oven for 35 minutes.