Note: Just watch the video, and at least give it to 0:20. It's catchy.
This is a video of Vocaloid (a brand of singing voice synthesizer software) Miku Hatsune (the 16-year-old anime girl with long, turquoise twintails that the voice is supposed to represent) performing the famous Levan Polkka in Japanese with Overwatch gun sounds synced to the song. The edit was created by Youtuber GameNut321, who said, "This was an easy edit, took roughly 6 hours." And may I say 6 hours well spent. I didn't expect to be into this, but I am into this. This song is like drugs to my ears. I could lay on the floor of a dirty work cubicle and listen to this for hours. "Isn't that what you've been doing?" Not if you're my boss!
Keep going for this video, a video of Miku Tasune singing it regularly without gun effects, and a group performing the original Levan Polkka in its native Finnish. Also, I'm fairly certain the original beat is where Daft Punk got the inspiration for 'Around The World'.
Thanks to Jennefer, for exposing me to this. Now if you'll excuse me, I have a rabbit hole to go down.