Rui (涙) is one of the main characters of Basilisk ~Ōka Ninpō Chō~. A young female ninja who uses the Butterfly technique to control the passions of men.
Rui is a young girl with brown-pinkish hair and violet eyes. She wears a sleeveless light colored kimono and ties it with a purple sash. She also wears an eye-patch on her left eye.
Rui is a very kind girl and rather quiet. Although she is quite unlike Utsutsu and Hachisu, in most situations she can stand up for herself.
Although not much is known of Rui‘s past before she met Namenba, she was staying at a shrine where she did different kind of chores.
While Namenba stayed at the shrine, the both of them developed a friendship and started to build a sister-like relationship. However, the shrine ended up being attacked by soldiers and when one of them tried to attack Rui who was using her ability, Namenba killed him and offered to take Rui with her. Rui immediately agreed after seeing Namenba's display of power. With all the maidens dead, Rui decided to leave with Namenba.
She then was brought up in the care of the Iga clan with Utsutsu and Hachisu so that she could become one of Hibiki's protectors and protect Hibiki at all costs.
The tears from Rui's left eye (often covered by an eye patch) provides her with a pheromone-like ability that incites the passions of men toward her. This power is materialized by glowing pink butterflies.
She is also skilled with kunais.
In the manga, she is depicted with different abilities. Her bodily fluids are shown to possess a strongly acidic or corrosive quality that can kill gargoyles created by Neiri Chiou and set human flesh ablaze.
Rui has a very strong friendship with Utsutsu. They are very close and often bathe together. In chapter 22 Utsusu said to Rui that she feel something for her like friend and keep his promise to show her his illusions and after that they die together.