It's called Boku wa Imouto ni Koi wo suru [I love my little sister]
More under the cut.
The manga, created by mangaka Kotomi Aoki, started serialization in "Shoujo Comic" (Shogakukan) in 2003 and continued for a long 2.5 years. The story, centering on the pure feelings shared between the siblings in this dangerous, incestuous relationship has gotten the sympathy of many teenage girls. The manga has sold more than 5 million copies.
I'm not really all the incest, BUT this movie looks really good.
I think the MatsuJun's acting's gotton ALOT better throughout the year, don't you think? ♥