Mikoto Takashiki is the titular character from Mikoto Nikki. She's the yandere for Matarou.
Ever since she was little, Mikoto has strived to be the best she can be. She was desperate to win her parents' approval, which she never received. At some point, she learned that her father was having an affair with another woman, leading to her resenting her life even more. The stress of trying to impress her parents eventually became too much for her to bear and she captured them one night. It's unknown how long they survived before they died from starvation. Not long after their deaths, she met Yukimaru who confessed his feelings for her. They dated for a while before Yukimaru went into her closet.
Mikoto tends to become overly attached to her boyfriends, hoping to be loved and understood by them. It's implied that she set up the diary scrap hunt to test their feelings for her. She's very sensitive to rejection due to a previous boyfriend, Yukimaru, discovering her parents' bodies in her closet. During one of the bad endings, she accuses Matarou of lying about his feelings for her before she chases after him. It's unknown if she kills him or if she takes him back to her house where she forces him to be with her forever. She is willing to lock up her boyfriends in the closet to ensure that they never leave her. Her behavior diminishes after Matarou accepts her. It's unknown what happens to Matarou in Bokko Youchien. It's possible that he either leaves Mikoto or if she kills him.
- In Yanderella, there's a business hotel that's owned by someone named Takashiki. It's unknown if the owner is Mikoto or someone in her family.
- A young Mikoto is briefly shown in Utsuro Nikki, she is said to be the cousin of the main protagonist.