“Is She U.N. Owen?” is probably the best-known piece of music from the vast Touhou Project, ((except possibly for “Bad Apple“)) and you can find innumerable versions in every style, from orchestral to nightcore, on YouTube. I stumbled across the one above recently while looking for something else.
Another version of the tune, impressive yet ridiculous.
Incidentally, “U.N. Owen” is not “Death Waltz.” This is “Death Waltz:”
Update: Yet another version of “U.N. Owen,” this one by Floating Cloud.