Hello Batoto,
I am looking for a manga I read once long ago. I searched for it using the advance filter, but was unable to locate it. Probably got genre inclusion/exclusions wrong. Anyways..
The story centers around a brother (mistaken as a sic-con) and his younger sister. His younger sister turns out to be a vampire(?) who uses a hair ribbon/tie to restrain her biting urges. It is the brother's attempts to cover for and help his sister that give him the label. That's basically the story as far as I remember. I never followed it, and I don't believe it's been updated in some time.
Thanks,
Koin.