Exactly! One of the things I find really cool about Japan is how doujin artists can really make it big, be it games (Touhou, Cave Story), music (livetune, supercell), or of course art/manga (find your own examples).
If you haven't heard of supercell before this, they're best known for their viral Nico Vocaloid songs, including Melt, World is Mine, Love is War (Koi wa Sensou), Black Rock Shooter, and When the First Love Ends (Hajimete no Koi ga Owaru Toki). I was pretty excited when I heard they'd be doing the ED for this series.
... yeah anyway I love the ED song. Speaking of which, posted this in the general topic too, but I may as well put the links here, too. Found this off of Nico.
Piano sheet music for the ED, "Kimi no Shiranai Monogatari"
Another version of "Kimi no Shiranai Monogatari"
Piano sheet music for the first OP, "Staple Stable"
If you can't read any Japanese, look for the links and buttons with the word ダウンロード (download) somewhere on them. You have to go through two pages to get the file.
Corresponding Nico vids: [
1][
2][
3]
And also a live performance of the first version of the ED sheet music. (I believe the vids that came with the sheet music were MIDIs)