User blog comment:B214/Volume 22 spoilers/@comment-2.220.205.251-20161130231234

This is just a theory but Bina Lessthan might be a reincarnated Chinese dragon. Dragons generally are a symbol of power and she is stronger than an average High-Class Devil; most likely stronger. She wears a dragon mask and in chinese culture the dragon is a symbol of fortune and prosperity and on the chinese new year, 90% of chinese people wear dragon masks for good fortune and prosperity for the current year. Bina has had very good fortune not making a mistake in her Rating Games getting 100% positive reviews and being Isseis peerage MVP. The mask itself is red, gold and blue and decorated with feathers and fur. Masks in chinese culture have different symbolisms depending on their colour and the colours of her mask hint at her personality. Red=loyalty, heroism and courage. Bina herself has obviously proven her loyalty to Issei by becoming his MVP by listening well to him. Gold=one of the coloured masks worn by demons as it adds a sense of mystery. Nobody but Issei and Ravel know who she is; she is a complete mystery as of now and she is a demon herself. Blue=wisdom, stubborness and fierceness. Bina is obviously quite wise to keep a flawless score of no mistakes so she is well trained in fighting. I think she will be stubborn as people who seem 'perfect' always are believing they cant make mistakes. Being a dragon already=being fierce in this series. So to sum up, Bina is a former chinese dragon and her mask and the connection between her now being a demon and gold masks in chinese being worn by demons as a symbol of mystery, as well as the symbolism of red and blue relating to what we currently know of her and her being quite powerful like dragons are, give evidence to this.