Start with the inspiration.

One of those spring days. It's grey and dreary from rain, making the green of the leaves brighter, the wet tree bark black. From this came thoughts of green, pistachio, pandan, what was I looking for? Green tea! And chocolate, and cherry. How should it go together? Have to try the ladyfinger batter with matcha idea. It comes out lovely, but dark, dark. How to brighten the look? I opt for a green tea buttercream even though I hate buttercream and find a gazillion other ideas after the fact - I even find an almost identical opera cake made with scientific precision on another site, with microthin layers of perfect cake and an absolutely smooth ganache top. Well, at least hers didn't have cherry. The cherry is a really good idea, so I add a whole one. Not bad for a first run, and I still have half a sheet of the matcha biscuit left...