There has been some confusion as to whether she is a Nukekubi or a Rokurokubi. Even though her detaching-head ability belongs to the Nukekubi, her official profile and title state that she is a Rokurokubi.
She could also be a Dullahan due to the similarities of head-detachment and her theme song having Dullahan in its name, but at the moment there is no clearly defined answer.
She is currently the only character who can 'dismember' a whole part of her body. In her case, it is her head.
She is also the only character whose mouth isn't visible in her official profile, since it's covered by her cape.
Sekibanki was shown in a 'sneak-peek' photo when Double Dealing Character was announced.
She is one of the few Touhou characters in the Windows series to not have a last name that is specified (the others being Rumia, Cirno, Chen, Kisume, Nazrin and Wakasagihime).
In Folklore, Nukekubi are said to have markings or symbols on their neck where their head detaches, revealing their identity. This might explain why Sekibanki wears a capelet around her neck.