Akiko Kusatsu is a first-year student at Shinyo Academy who appears in the Boogiepop and Others storyline. Before the events that define her role, she is presented as a normal and cheerful girl. Her ordinary life takes a dark turn due to her romantic feelings for a classmate, Masami Saotome. Akiko develops a crush on Saotome, a decision that proves to be tragically misguided and ultimately leads to her downfall. Her feelings for him make her vulnerable, as she is portrayed as somewhat gullible and trusting of him without recognizing his true intentions.

In terms of personality, Akiko initially appears as a typical, pleasant young student. However, this changes drastically after she becomes a victim of Saotome and the entity he serves, the Manticore. During what she believes is a date, Saotome secretly spikes her drink. He then takes her to the Manticore, a creature that consumes human essence. The Manticore does not simply kill Akiko; instead, it transforms her into a human puppet. After this process, her emotions and self-control rapidly erode and disappear, leaving her as a mindless servant. Her cheerful disposition is completely replaced by an empty, lifeless obedience to the Manticore's commands.

Akiko's motivations are stripped away following her transformation. As a puppet, she no longer possesses personal desires or goals, acting solely on the orders of her master. Her primary function in the story is to serve the Manticore's plan to find more victims. Under these orders, she spreads a drug known as Type-S among her classmates. Her role is to lure and prepare other students, like Kyouko Kinoshita, to become the Manticore's future prey. She becomes an instrument of manipulation and destruction within Shinyo Academy, directly contributing to the wave of disappearances and strange occurrences that other characters are trying to solve.

Her key relationship is with Masami Saotome, the boy she admired and who betrayed her trust completely. He is not a love interest but her predator, using her affection to deliver her to the Manticore. After her transformation, she has no genuine relationships, only a master-servant dynamic with the Manticore. Her interactions with other classmates become predatory, as she approaches them not as a peer but as a tool to administer drugs and identify new targets. The development of Akiko Kusatsu is a tragic and short arc. She begins as a lively individual, is victimized, and undergoes a horrific change into an empty shell. Her character does not grow or recover; instead, she devolves further into a state of being a zombie-like puppet. Eventually, the Manticore deems her no longer useful, as the process of her transformation has used up too many of her brain cells, making her incapable of functioning properly. At this point, the Manticore kills her, discarding her without any further consideration. Regarding notable abilities, as a human puppet, Akiko does not display any superhuman powers. Her ability to function is solely derived from the Manticore's control, allowing her to move and speak just enough to carry out orders. Her most notable ability within the narrative is her capacity to appear normal to her peers, which enables her to deceive them into taking the Type-S drug. This semblance of normality is her primary tool for carrying out the Manticore's will.