"Death Waltz" is a common misnomer for the black MIDI version of "Last Brutal Sister Flandre S", COOL&CREATE's "U.N. Owen was Her?" remix. Many mistakenly call it "Death Waltz", a substring of the title of an entirely different, tongue-in-cheek piece by American composer John Stump and "arranged by accident". John Stump's "Faerie's Aire and Death Waltz" is featured in the first half of this YouTube video by user Ryan TTC (TheTrustedComputer).
On October 25, 2011, YouTube user Marc posted a video improperly titled "Impossible Piano Song - Death Waltz (U.N. Owen Was Her?)". It is said that this is how the genre of black MIDI reached YouTube.