As the title suggests, the male protagonist travels from a lightly male-dominated world to an ABO world. There is no bisexuality, the organs that differentiate between women and men are used only for urination and excretion, sexual intercourse occurs only in the glands, and reproduction occurs through the abdominal slit. Beta is a pheromone with high concentration that causes low pregnancy. When everyone is born, they are only divided into female and male, that is, they have no gender. Alpha accounts for 15% of society and is only developed by females. Theoretically, there is a possibility that a male will develop into an Alpha, but the probability is about one in a trillion. It usually develops between the ages of 12 and 14. Betas make up 75% of society, 35% are female Betas, and 40% are male Betas. It usually develops between 6 and 8 years old. Omegas account for 10% of society and are only developed by men. The probability of a woman developing an Omega is one in nine billion. It usually develops between 9 and 11 years old. The average lifespan of an Alpha is 347·6 years, that of a Beta is 163·1 years, and that of an Omega is 30·2 years. Alpha despises Beta and extremely objectifies Omega. Due to excessive fertility and Alpha's tyranny, Omega's lifespan is so short. In order to avoid unnecessary resistance, all males will not receive any education before development. If they have not developed into Beta, they will be sent to Omega training centers together. Omegas are regarded as objects. They cannot speak Alliance language, let alone writing, and have low intelligence. Male Betas are physically stronger than female Betas and have lower intelligence than female Betas. Female Betas are more creative and rebellious. Female Betas are dominant among Betas and almost all have homosexual tendencies, but the birth rate of same-sex unions among Betas is very low. As for the male protagonist, unfortunately he developed into an Omega.