|Oh dear... That's not very good.|
Tsukiko Sagi (鷺 月子 Sagi Tsukiko) is one of the central characters in the plot of Paranoia Agent. She is rather lackadaisical, prone to daydreaming, and never seems to be quite completely "there", possibly indicating an avoidant personality disorder. She is a character designer who has created a Hello Kitty-esque mascot known as Maromi; Tsukiko always keeps her plush toy version of Maromi on her person. Ever since her Maromi design, she never seriously takes her job to design a new character, no matter how much she is asked by her superiors to submit a new character design. She is Lil' Slugger's first apparent victim in the series, and the catalyst which jump-starts the plot. When Detectives Ikari and Maniwa are brought in and Tsukiko is questioned, she seems to become even more introverted than before; Ikari suspects that she may be withholding information. As it turns out, he's more correct than he could have ever imagined.
The actions of Tsukiko Sagi are a major mover throughout the series. She often speaks with her Maromi plushie, who more than often magically comes to life – Maromi is in practice her familiar. In any case this apparition gives the viewer yet more evidence that something is not quite right with Tsukiko.
Tsukiko's name means "Moon Child" or "Little Moon", a reference to the Japanese folklore tale of the Kaguya Hime; in some languages, "little moon" is also the term for "lunacy". Her last name, Sagi, references a type of bird. Birds are often associated with being free spirits, but also being hopelessly awkward and strange. It has also been suggested that the combination of her full name, read in Western order (Tsukiko Sagi), can be analogous to the English term "looney bird", making another pun in reference to lunacy.
It is interesting to note that "Sagi" is also Japanese for "fraud", which explains much of how Lil' Slugger is later revealed as being created by Tsukiko.