Preheat oven to 325. Butter and flour two 8” cake pans.
Beat butter, sugar and coconut oil together until light and fluffy – about 5 minutes. Add egg whites one at a time, beating for a good 2 minutes after each addition. Scrape down bowl. Add the salt, vanilla, sakura extract, and baking powder and beat well. Scrape down bowl. Sift in flours, fold a bit with a spatula so it doesn’t make a mess when you turn the mixer back on, and with mixer on low, slowly pour in buttermilk. Mix until just combined. Fold in pink sprinkles and ensure all batter is homogeneous by scraping the bottom of the bowl.
Add some of the white batter to the bottom of each pan and smooth it down - just enough to make a 1/2 inch layer.
Grab your piping bag with the chocolate batter and snip off just a bit so you have a small opening. You’ll squiggle it (this is the best word I can think of to describe it, see pic) around the batter, shaking it as you go and overlapping (don’t make straight lines) so that it kind of looks like branches that are intertwined. Don’t overdo it or it will weigh down the center of the cake.
Add more white batter, smooth the top down very gently without disturbing the squiggles and pipe more squiggly lines.
Repeat until all the batter is equally distributed between the two pans.
Bake cakes for 40-50 minutes. Let cool for 5 minutes in the pan and then invert onto a cooling rack.