Mushi Pan variations for dough and topping?

I'm in love with Mushi-Pan right now and I also tried my own one some days ago! I also made some Matcha-butter-cream and Sesame-peanut-cream as a topping. It was delicious, but I want to try more flavors. Do you have any tips for me how to variate the Mushi-Pan-dough a little bit? What is your favorite-Mushi-Pan ingredient? (for example, chocolate, fruits or any other cream as a topping...?) Thx for all your help! =D
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