Frolbericheri Frol belongs to an alien species where biological sex remains undifferentiated until adulthood, a developmental stage called "menir." Consequently, Frol lacks defined male or female physical traits during adolescence. Originating from a patriarchal and misogynistic society, only the eldest children are permitted to differentiate into males. This structure creates a gender ratio of roughly five or six females per male, with men holding power and women assigned labor-intensive roles. Remaining on their home planet would force Frol to develop into a female. To escape this fate and gain the right to become male, Frol takes the entrance exam for a prestigious space academy. Passing represents their sole chance to achieve autonomy over biological development.

Physically, Frol possesses long hair, delicate facial features, and a petite stature, traits others perceive as conventionally feminine. This leads to immediate gender misidentification when Frol removes their helmet upon arriving at the derelict spaceship exam site. Multiple crew members assume Frol is female, a misconception Frol vehemently rejects with anger and offense. Frol explicitly identifies as male, utilizing the highly masculine Japanese first-person pronoun "ore" and expressing disdain towards women. Another applicant, Tadatos Lane, who possesses an intuitive lie-detection ability, confirms Frol's statement about being a man is truthful.

A pivotal moment occurs during an accidental exposure in the shower, revealing Frol's body to a crew member. Despite observing a flat, masculine-appearing chest, the crew member designates Frol as female based on overall appearance and demands an explanation. This prompts Vidmenir Knume, a nonhuman crewmate, to explain Frol's menir status. Knume clarifies that within his culture, a menir develops sex characteristics naturally over time, but for Frol's species, this development is artificially induced. Frol's reaction to the crew's surprise, including asking Tada how long he has been male, suggests possible unawareness that a non-menir developmental path is the norm for other species.

Frol's primary motivation throughout the exam is escaping the oppressive gender roles of their home society, particularly the subjugated status of women, rather than an innate gender identity. Their insistence on being perceived as male and despair at becoming female stem from internalized misogyny and avoiding disenfranchisement. Frol actively participates in the group's survival efforts during the exam, demonstrating intelligence and tenacity. Ultimately, Frol passes the examination, earning the right to become a spaceship pilot and escaping the mandated societal role.

Following success, Frol undergoes a significant shift. Frol decides to develop into a female and expresses the intention to marry Tadatos Lane. This decision arises after Lane offers marriage should Frol be forced to become a woman, an offer Frol accepts once the threat of enforced gender roles is removed by passing the exam. The conclusion ties Frol's embrace of womanhood directly to the prospect of marriage.