If I wanted to be cynical and/or pretentious, I might draw a parallel between the infant-like nature of Hello Kitty products, the Freudian childhood wish that might indicate, and the fact that her asking you to buy something rather than buying it herself portrays an interesting father/daughter dynamic. But that would be truly weird, and wait, are we still on HN? OK I'm disoriented now.
Seeing as my wife and I share all funds, it would not be "me" buying "her" something, as us having a discussion as to whether this was an acceptable purchase.
HK is huge in Asian countries especially, which is where my wife is from- I readily admit to confusion over HKs appeal.
BTW did you know that HK is the weight of 3 apples and the height of 5 apples?
