Misa Amane, also known as Misa-Misa, is a prominent character who becomes the second individual to wield a Death Note. Her background is marked by tragedy; she was born in Kyoto on December 25 and worked as a popular model and actress before the main events of the story. When she was a teenager, she witnessed a burglar murder her parents in her own home. The killer managed to evade conviction through legal technicalities, but was later killed by the person known as Kira. This event fostered an intense, unwavering sense of gratitude and devotion in Misa, who saw Kira as a divine agent of justice.

Her personality is outwardly cheerful, impulsive, and somewhat childish, often referring to herself in the third person. She has a strong temperament and can become easily jealous, particularly regarding Light Yagami, for whom she quickly develops an all-consuming romantic obsession. Beneath this bubbly facade, however, is a ruthless determination. She is not intellectually gifted in the same way as the series' masterminds, which makes her vulnerable to manipulation, but she possesses a strong will and a willingness to sacrifice anything to achieve her goals.

Misa's primary motivation is to meet, assist, and earn the love of Kira, whom she discovers is Light Yagami. To accomplish this, she uses a Death Note given to her by the Shinigami Rem, which originally belonged to another Shinigami named Gelus. Gelus had fallen in love with Misa from the Shinigami realm and sacrificed his own life to save hers by killing an obsessed stalker. Eager to find Kira, Misa makes a contract with Rem, trading half of her remaining lifespan to gain the Shinigami Eyes, which allow her to see any person's name and lifespan simply by looking at their face. This ability makes her a powerful asset, as she can kill without requiring a name to be provided by someone else.

In the story, Misa acts as a formidable but chaotic ally to Light. While he plans and manipulates from the shadows, she acts on her impulses, which sometimes puts both of them in danger. She is instrumental in various schemes, such as confronting the Yotsuba Group, but her carelessness also leads to her capture by L, forcing Light to intervene. Her key relationships are extreme and defining. Her love for Light is absolute and one-sided; he views her as nothing more than a useful tool, a fact he makes clear to her, but she willingly accepts this role, believing she can eventually win his true affection. In contrast, she forms genuine bonds with the Shinigami, particularly Rem, who grows to care for her deeply and ultimately sacrifices her own life to protect Misa from being used by Light to kill L. She also develops a strangely amicable, if combative, relationship with L, whom she often calls a pervert.

Misa undergoes significant development, though it is largely a descent into deeper obsession. She willingly trades half of her remaining lifespan for the Shinigami Eyes not once, but twice, reducing her life to a quarter of its original span. On Light's orders, she twice relinquishes ownership of her Death Note, losing all her memories of being Kira each time. Without her memories, she is simply a loving girlfriend, but her devotion is such that she immediately returns to her role when her memories are restored. After Light's final defeat and death, Misa is last seen on the edge of a skyscraper, looking towards the sunset. The manga's author has speculated that after learning of Light's death, she fell into despair and committed suicide, with her suggested death date being over a year after his.

Her most notable ability is the Shinigami Eyes, which provide instant knowledge of any person's name and lifespan. This power comes at the great cost of half of her remaining life each time she acquires it. Aside from this supernatural trait, she is a skilled actress and model, using her fame to gather information and access areas that would otherwise be unavailable to her, demonstrating a cunning that is often overlooked due to her otherwise naive nature.