Fushigi Purupuru Pururin Rin!   by Shishidou Rumi.
N.H.K ni Youkoso! Sound Collection - Sunny Side ni Youkoso!
Track 08

Fan-made artwork by Wszechobecniak:
http://wszechobecniak.deviantart.com/art/Pururin-16-119553390

Now available in 4K (UHD 3840x2160) master race. Audio is in lossless FLAC.
It was necessary to be future-proof.

Explanation:
"4K" is a resolution, and still images have resolution too. There's absolutely nothing wrong about having a 4K still image, since it looks better than the same image at a lower resolution.

You may not know, but YouTube used to process the audio quality depending on the video resolution. This means 480p videos had worse audio quality (lower bitrate) than 720p videos, per example.

In order to enjoy the best quality YouTube could offer, I chosen the highest resolution possible that was available back then, and merged it with a lossless copy of the audio. I know YouTube doesn't allow lossless audio but, if you upload it lossless, the audio is only encoded to a lossy format…