Mix warm water and matcha powder in a container until fully dissolved without lumps.

In a bowl, crack the egg, remove the chalaza, and whisk with granulated sugar until pale and fluffy.

Add milk and the dissolved matcha mixture to the egg mixture, then sift in pancake mix and fold gently with a spatula.

Heat a tamagoyaki pan, cool it slightly on a damp cloth, then pour in the batter over low heat.

Cover with aluminum foil and cook for 5 minutes. Remove and wrap in plastic wrap to cool.

Whip heavy cream in a bowl until stiff peaks form, then fold in red bean paste to make azuki cream.

Unwrap the cooled sponge, spread azuki cream on top, and roll tightly using the plastic wrap.