"Nandeyanen" is a comedic anime series that revolves around the misadventures of a young boy named Taro Yamada, who discovers he is the reincarnation of a legendary samurai from the Sengoku period. The story begins when Taro, an ordinary middle school student, is visited by a mysterious spirit claiming to be his past-life self. This spirit, a brash and eccentric samurai named Nobunaga Oda, insists that Taro must fulfill his destiny by reclaiming his former glory and protecting Japan from an ancient evil that has resurfaced.

As Taro reluctantly accepts his role, he is thrust into a series of absurd and chaotic situations. Nobunaga, now a ghostly companion, provides guidance—often in the form of over-the-top and impractical advice—while Taro struggles to balance his newfound responsibilities with his everyday life. The narrative explores themes of identity, duty, and the clash between modernity and tradition, as Taro navigates school, friendships, and family while battling supernatural foes.

The main cast includes Taro’s childhood friend, Yuki, who becomes an unwitting ally in his quest, and a rival classmate, Kenji, who harbors a secret connection to the ancient evil. The antagonist, a malevolent entity known as the Dark Shogun, seeks to harness the power of the past to plunge the world into chaos. Throughout the series, Taro and his companions encounter a variety of historical figures reincarnated as quirky characters, each contributing to the comedic and episodic nature of the plot.

The series blends slapstick humor, historical references, and supernatural elements, creating a lighthearted yet engaging narrative. Taro’s growth from a reluctant hero to a more confident individual forms the emotional core of the story, while the dynamic between him and Nobunaga provides much of the comedic relief. The episodic structure allows for a mix of standalone adventures and overarching plotlines, culminating in a climactic battle against the Dark Shogun that tests Taro’s resolve and understanding of his dual identity.