In a world where humanity has diverged into four distinct races, ordinary humans called Niers coexist with those carrying the blood of beasts. The latter are classified as Vamps, who possess the genes of sky beasts; Lycans, who carry the genes of land beasts; and Sirens, who inherit the genes of water beasts. These three groups are collectively known as Beasts of Blood, or B.O.B.s, and each retains unique ecologies and biological traits. Haruka is a Nier, the most common race, who has spent his life supporting his eccentric father and weathering his spontaneous, often chaotic decisions. His father’s latest surprise is a sudden marriage to a man who has three sons of his own, all close in age to Haruka. The catch is that all three are B.O.B.s. Haruka, a naive and sheltered Nier, finds his ordinary life turned upside down as he moves in with his new step‑brothers, each possessing vastly different abilities, instincts, and social dynamics. As he navigates the unfamiliar social and romantic tensions within this blended family, the story explores themes of acceptance, desire, and the clash between human norms and beast‑blood instincts, with a focus on the developing relationships between Haruka and his alluring, otherworldly step‑brothers.