Buzam A. Calessa, almost universally referred to as B.C., serves as the sub-commander and second-in-command of the pirate ship Nirvana. She is a stern, disciplined, and work-oriented individual who presents an austere and all-business demeanor, often acting as the strict enforcer of responsibility and order on the bridge. A skilled tactical officer, she gives commands firmly and decisively, coordinating the ship's defenses and assaults during combat situations. Despite her rigid exterior, she is not without compassion and demonstrates a clear concern for the well-being of the crew. Her proficiency extends to close-quarters combat, where she favors using a whip with notable dexterity.

Throughout much of the story, B.C. is a figure of quiet authority and efficiency. However, her actions are occasionally marked by an air of secrecy, such as when she is observed discreetly removing a data disc from the ship's database when she believes no one is watching. These enigmatic behaviors build toward the central revelation about her character in the second stage of the narrative. It is disclosed that B.C. is not who she appears to be; her true identity is Tenmei Uragasumi, a male intelligence officer and commander from the male-dominated planet of Tarak. As a spy, he was assigned to infiltrate the Nirvana and gather intelligence on the women from Mejare. To facilitate this deep cover mission, he underwent a complete sex change and uses a small, green jewel-like device on her necklace to modulate her voice to sound female.

This revelation places B.C. in a precarious position, caught between her original mission and the genuine bonds she has formed while serving on the Nirvana. The experiences she shared and the trust she built with the crew, particularly with the ship's elderly captain, Magno Vivan, ultimately prove to be more powerful than her loyalty to her homeworld. Instead of betraying the Nirvana, she remains loyal to the crew. In the end, Captain Magno forgives her for the deception, allowing her to retain her position as sub-commander on one firm condition: that she continues to exist as B.C.. She commands the Nirvana in the final battle and is later seen participating in the selection of new candidates from Tarak to live alongside women.

One of her key relationships develops with Bart Garsus, a young male crew member from Tarak. Bart becomes enamored with B.C. and repeatedly attempts to initiate a romantic relationship, though she gently rebuffs his advances. When Bart later discovers the truth about her original gender and identity, he remains fundamentally unaffected in his feelings and continues to pursue a connection with her. This subplot highlights the complex themes of identity and acceptance that surround her character. While the anime presents B.C. with this complex backstory as a male spy who transitioned to female, alternative versions exist in other media; for instance, in the manga adaptation, B.C. is depicted as biologically female and serves as an antagonist.