"The solitary Vampire": "Souleater". At least from the art style and character design - I didn't read enough of it to say anything about the plot.
Also, why do you guys all assume the siscon manga is supposed to be OreImo? None of the scenes fit, and the plot doesn't fit either
as Kyousuke is never torn between morality and his feelings - he isn't even aware of any romantic feelings towards Kirino until the final arc, and then quickly figures out that he's adopted (VN version, the LN only hints at this) and gets his good end.
Rather, I'd guess it's "Usagi Drop", as the art style, the character's posture and all but one scene fit.