Makino Yui 牧野由依 does the piano accompaniment in a preview clip for the fall anime Sketchbook ~full color'S~, in which she plays one of the main characters. She will also sing the ED.
You can see the preview clip on the show's homepage. Click the little white banner near the top middle of the page, with the red stripe on the left of it.
Yui says in her blog that she was just asked in an impromptu way to do the preview accompaniment, and she chose to use a tune from Brahms. She said she tried to give it a nostalgic quality like hearing music filtering out of the practice rooms after school. She is currently a fourth-year piano student at a Tokyo-area music university.
Makino-san started playing piano at the age of three, and did piano accompaniment to films while still a child. She also appeared in two films, several commercials, and a TV drama, according to Japanese Wikipedia.
She has had five different radio shows, and as a singer has put out four singles and an album. She sang the OPs for both ARIA series. She turned 21 in January of this year.
There are a number of Makino Yui PVs on YouTube here and here, as well as clips from a recent series of appearances in China, and there is an interview with her about her musical work for ARIA here.
Her seiyuu debut was as Sakura in Tsubasa Chronicle in 2005. She was nominated for best young seiyuu of 2006 for her outstanding portrayal of Misaki in Welcome to the NHK.
She is doing a nice job with the character Lapis in recent episodes of Kaze no Stigma. Her seiyuu voice has a unique quality I love: a kind of fresh directness and intimacy, and somehow almost a boyishness.
On her home page, she says her favorite musical artists are film composer Ennio Morricone and French classical pianist Pascal Rogé. Here are her pages on ANN and Wikipedia, and here is her homepage.