I admit to having learned to be a little defensive when I talk about bean paste in dessert recipes, after the guy at the anime club tried my dessert onigiri (another Orihime-like invention in that I came up with them before I knew that you weren't supposed to be able to use bean paste with regular rice/gohan, just with mashed glutinous rice/mochi).
He thought they were awesome and asked what was in them. I said cheerfully "Oh, bean paste and pie cherries."
He replied in a horrified voice that echoed throughout the entire building, "BEAN PASTE?!" (as though I'd just said 'live snails' or something).
So yeah, bean paste actually is a legitimate dessert ingredient in Japan (and actually it's pretty hard to find a Japanese sweet that doesn't involve either mochi, bean paste, or green tea). I tend to forget how bizarre it sounds to Westerners until I tell my friends what the ingredients in this cake concept are and they blink at me a lot and start laughing, though... XD