What is the name of the song playing at 10:25? The anime is "Zetsuen no Tempest", in the last episode (#24).

I recall hearing the song even in Kuroshitsuji (Black Butler).
The piece playing at 10:25 in episode 24 is track #9 "Kusaribe" from the second volume of the OST. 10:25 in the episode corresponds to roughly 0:21 in the track. Here is an excerpt (0:18–0:28): https://clyp.it/kouhf2vp.

I have not seen Kuroshitsuji, but I find it vanishingly unlikely that you would have heard this particular piece in it. (All the more so given that Kuroshitsuji's music was apparently composed by Iwasaki Taku, and this piece is stylistically very unlike most of his work.)