"Happy World!" is a supernatural romantic comedy manga that centers around Tsurugi Bishou, a high school student whose life takes a bizarre turn after a series of unfortunate events. Tsurugi, once a cheerful and optimistic individual, becomes plagued by bad luck following a tragic accident that claims the lives of his parents. His misfortunes escalate to the point where he contemplates ending his own life. However, his suicide attempt is interrupted by the sudden appearance of a mischievous and eccentric angel named Lapis, who claims to have been sent to Earth to bring happiness to humanity.

Lapis, despite her divine origins, is far from the typical image of a benevolent angel. She is clumsy, self-centered, and often causes more problems than she solves. Her arrival in Tsurugi's life introduces a chaotic dynamic, as her attempts to improve his situation frequently backfire, leading to comedic and often absurd situations. Despite her flaws, Lapis is determined to fulfill her mission, and her presence gradually begins to alter Tsurugi's outlook on life.

The narrative explores the evolving relationship between Tsurugi and Lapis, as well as the challenges they face together. Tsurugi's initial skepticism and frustration with Lapis slowly give way to a deeper understanding of her intentions, even as her antics continue to disrupt his daily life. Alongside Lapis, Tsurugi encounters other supernatural beings, including demons and rival angels, each with their own agendas and quirks. These interactions further complicate his life, blending humor with moments of introspection and emotional depth.

As the story progresses, Tsurugi's journey becomes one of self-discovery and resilience. The manga delves into themes of redemption, the search for happiness, and the complexities of human emotions. While Lapis remains a central figure, Tsurugi's relationships with other characters, including his classmates and family, also play significant roles in shaping his experiences. The balance between comedic elements and heartfelt moments creates a narrative that is both entertaining and thought-provoking, offering a unique take on the supernatural genre.