What's the music that plays at the end of ep. 22 of Shigatsu wa Kimi no Uso?
The piece is called "31 - Kimi ga Iru"
It is in the OST album for the anime, Disc 1.

Followed by "05 - Kirameki ~Kousei to Kaori no Ensou Ver.~" from the ED single "Kirameki" album.

So basically it starts off as Kimi ga Iru, then Kirameki chimes in.

The piece before that is "17 - Kouiu Kimochi wo Nante Itta Kana" if you're interested.