Preheat the oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
In a large mixing bowl, sift together the all-purpose flour, granulated sugar, cocoa powder, baking powder, baking soda, and salt.
Add the eggs, whole milk, vegetable oil, and vanilla extract to the dry ingredients. Beat on medium speed with an electric mixer for 2 minutes until smooth.
Carefully stir in the boiling water. The batter will be thin; this is normal.
Divide the batter evenly between the prepared cake pans.
Bake for 30 to 35 minutes or until a toothpick inserted into the center comes out clean.
Remove the cakes from the oven and allow them to cool in the pans for 10 minutes. Then remove from pans and cool completely on wire racks.
To make the frosting, beat the softened butter in a large bowl with an electric mixer until creamy.
Gradually add the powdered sugar and cocoa powder, beating on low speed until combined.
Add the milk and vanilla extract, then beat on high speed until light and fluffy, about 3 minutes.
Divide the frosting into three portions. Leave one portion white, tint one portion pink with the pink food coloring gel, and tint the last portion light blue with the blue food coloring gel.
Place one cake layer on a serving plate. Spread a layer of white frosting evenly on top.
Place the second cake layer on top and cover the entire cake with a thin crumb coat of white frosting. Chill for 15 minutes.
Use the pink and blue frostings to pipe kawaii-style decorations such as cute faces, bows, and hearts on the cake surface.
Add mini marshmallows as cheeks, edible candy eyes, and white chocolate chips as noses or accents to enhance the kawaii appearance.
Refrigerate the decorated cake for at least 30 minutes before serving to set the frosting.