Non-creative ideas (meaning - people have already done it before):
Sesame paste, green bean paste, ice cream, strawberry and chocolate, chocolate, peanut butter, finely crushed peanuts, chestnut paste, custard, and fruit jelly. These are just some sweet fillings for mochi/daifuku.
Jelly - Kiwi-strawberry, pineapple banana, pineapple coconut, apple and strawberry peanut butter.
Others - Cheesecake, cream puff, chocolate mousse, mango mousse, french roast kahlua mousse, raspberry chocolate mousse, chocolate coated marshmallow with crushed nuts, chocolate coated banana, dark chocolate coated crushed oreo ball, mille-feuille...
If you do not insist on using fillings and your mind is not set on mochi/daifuku, you will expand your options. Mochi could be grilled and deep fried too. Mochi could also be used in stews and hot pots. If you want to include Chinese rice flour related dishes, you'll run out rice flour very quickly. :D