Bites the Dust in theory is supposed to kill anyone who finds out about Kira's secret and then reset the day a la All You Need is Kill until everyone who could potentially pose a threat to Kira is dead. The wrinkles in its power are that Kira's knowledge of the reset seems to vary from chapter to chapter (and really, this would only be a worthwhile power if he could remember what happens during each loop) and that even after killing off the entire main cast of Part 3 it continues to reset the day, which makes me think that it was initially written without the "resets the day" part in mind, instead just serving as a fool-proof way to safeguard Kira's secret. The way it's ultimately written is interesting, but kinda sloppy.