I very rarely use the work ‘beautiful’, but in the case of this song, I think it’s apt. Kimi no shiranai monogatari by Supercell, the closing theme for Bakemonogatari (which is well worth watching in its own right, hosting some other catchy music as well as having a unique visual style).
(Turn on captions and up the video quality for great justice)
A delicious sound, and I also like the allusion to Tanabata (in referring to the Summer Triangle). Taken in the context of Bakemonogatari, the power of the lyrics is only increased.