Blue Beard is a seemingly stern and intimidating man. He was courting Amalie, but she didn't like him. It turns out that Blue Beard was married previous to several other women, and all of them mysterious disappeared. Through some weird coincidence Ludwig looks almost exactly like his first wife. Blue Beard is oblivious to the fact that Ludwig is a guy and takes him back to his castle. There Ludwig finds out that Blue Beard's beard is a fake. The beard helped Blue Beard become another person because without it he was a weakling who cried easily. Ludwig also discovers that Blue Beard murdered all of his previous wives. He had given his wives keys to every room in the castle, but forbid them from going into a certain room. His first wife, Annie, disobeyed him and went into the room anyway and discovered his secret about the beard. Annie felt that it was not the beard that magically made him not a weakling, but himself. She wanted to Blue Beard to step out as himself, but Blue Beard felt that she purposely wanted to disgrace him--so he killed her. The very same fate fell upon each and every one of his wives after that. Blue Beard attempted to kill Ludwig as well after finding out his secret, but is impaled by a weather vein in a freak accident. Using his last breath he regretted ever killing Annie because she was the only women who had ever loved and accepted him for who he was.
Designed to be a general-purpose, if beautiful, tool for Kabapu, Ropponmatsu (Unit 1) excels in bomb-disposal. After failing in her first mission, she is given an additional form (Unit 2), that of a perky, young cat-girl. In the original manga, only one Ropponmatsu unit is active at any one time; the reason for this is later revealed to be that there is only one central "core" that is switched between the two bodies. Kabapu attests that the core contains the soul of the princess of the lost civilization of Solaria, and he has had the Ropponmatsu body created to house it as part of his plan to destroy all remaining traces of Solaria's technology. Conversely, the anime (produced before this revelation occurred in the manga), has the Ropponmatsus appearing as two distinct entities who frequently cooperate on important tasks. Although they have a tendency to be destroyed on their missions, Shiouji keeps a lot of spares, which play a large role in the penultimate episode of the series). The vast difference between the units leads to some tension between Kabapu and Shiouji: both incarnations of Ropponmatsu have a tendency to fail in the course of their duty, due either to extreme mass (Unit 1) or lack of appropriate functionality (Unit 2).
She is introduced in episode 3 as an assistant of sorts to the Female Informant from Episode 2. Much like her predecessor, she demands sex with either Rin or Mimi for information. Although, her first encounter with Mimi was less than romantic, by episode 4, they appear to have entered into some sort of relationship. After episode 4, she has apparently died.