Otoya Takechi

Otoya Takechi also known as Jack the Ripper of the 21st century, she is main antagonist in the episode three of the animes series Akuma no Riddle, already in the tenth episode, she act more as secundary antagonist. She is a serial killer that terrified the population, although her do part of Black Clash, by the fact if she wins would go win a request, even after having the chance to redeem helself and go to the good side and befriended Haru, she refused and continue with her hunt for sadistic pleasure.

Biography
Nothing is known about Otoya's past or how she became a Assassin, or how she got the tittle of Jack the Ripper of the 21st Century, after she killed 29 people mutilating them with scissors. She has no record of her previous life or that of her family, yet there is a theory within the anime universe that she murdered her entire family, and a detective was investigating to get her. Even part of that was the reason she joined Black Class.

The Notification
Otoya was the first assassin to attempt to kill Haru after writing II'I kill you.

Assassination attempt
Later, Otoya and Haru are talking on a bench sitting, Otoya gives a bouquet of flowers to her, saying that she is protecting her from Shiena, more suddenly, she says that everything she said to her lies and throws the bouquet on Haru's face making her faint. Otoya then takes Haru to a botanic garden as the class had been the day before, she then tortured slowly getting to have a sadistic pleasure with it. Otoya listens to the bullfinch on her cell phone, while she tries to talk to her that she is being tortured by Otoya, she discovers where Haru is because Mizorogi has taught them about the bullfinches. Otoya then finds the place where Haru is smitten and is close to giving the final blow, but Tokaku appears and cuts with a shot in the face of Otoya scarring his face, Otoya simply goes towards Tokaku blocking his bullets and defeating her, however, when she was about to give the final blow she is poisoned by Haru for the same bouquet flowers she used against Haru. She remained unconsciouns, until the whole time until tomorrow, when Nio arrived informed that she was expelled that she should leave Otoya then tries to convinces her without success, then Otoya tries to stab her with her scissors more Nio deviates and easily defeats her taken out of school ad possible trapped in prison despite not showing it.

Escape in Prison and Return
After stabbing a guard with his scissors and fleeing from the prison Otoya then returns to school to take revenge on Haru, she goes to school more is caught and held against her will by Sumireko Hanabusa. During the attempt on the murder of Haru, Otoya gets loose with a knife and one of idea about killing Haru and tries to kills Hanabusa but she wakes up more is confronted by Nio Hashiri that hypnotizes and is arrested again.

Last Episode
In the final episode, Otoya appears doing forced labor in a garden and singing waiting to be released.

Trivia

 * According to Otoya her bithday is on December 31 or January 2, so her birthday is on March 10.
 * His personality reminds a lot of Joker, both are psychopaths cross the Moral Event Horizon with facility.