"Widow" is a psychological thriller anime that centers on a young woman named Aya, who becomes entangled in a web of mystery and danger following the sudden death of her husband, Hiroshi. The series begins with Hiroshi's unexplained death, which is initially ruled a suicide. Aya, however, suspects foul play and begins to investigate the circumstances surrounding his demise. Her search for the truth leads her to uncover a series of dark secrets about Hiroshi's past, including his involvement with a clandestine organization known as the "Black Veil."

As Aya delves deeper, she encounters a diverse cast of characters, each with their own hidden agendas. Among them is Kaito, a former colleague of Hiroshi who claims to have information about the Black Veil but is reluctant to share it fully. Another key figure is Rina, Hiroshi's estranged sister, who harbors resentment toward Aya and seems to know more about Hiroshi's activities than she lets on. The narrative also introduces Detective Saito, a law enforcement officer who becomes both an ally and a hindrance to Aya's investigation, as his own motives remain ambiguous.

The plot unfolds through a series of flashbacks and present-day events, revealing Hiroshi's double life and his connections to the Black Veil, a shadowy group involved in illegal experiments and political manipulation. Aya's journey is fraught with danger as she uncovers evidence of corruption, betrayal, and a conspiracy that reaches far beyond her initial suspicions. The tension escalates as she realizes that her own life is at risk, and she must navigate a treacherous landscape of deceit to uncover the truth.

Themes of trust, loyalty, and the consequences of obsession are explored as Aya's investigation brings her closer to the heart of the conspiracy. The series maintains a steady pace, balancing moments of intense action with quieter, introspective scenes that delve into the characters' motivations and relationships. By the end of the series, Aya's relentless pursuit of justice leads to a climactic confrontation that resolves some mysteries while leaving others open to interpretation, creating a sense of lingering unease and ambiguity.