Mariandale is a transgender woman who serves as the personal maid and bodyguard of Princess Ecarlate Juptris Saint Piria in the kingdom of St. Piria. Born the younger of two siblings, she grew up in fear of her older brother, who later became a fierce mercenary. At some point she took on the role of a combat maid and was assigned to protect the princess during her journey to an arranged marriage that would unite kingdoms and prevent war. She also founded an underground rebel group called AEG (Anti-Empire Girls), which fought for the rights of those who wished to present themselves femininely or become women. Mariandale is confident, flirtatious, and enjoys cooking, drinking, romance, and wearing pretty clothes. She is completely unselfconscious about her identity as a trans woman, stating that she lives as a woman simply because she wants to. This self-assuredness makes her popular among both men and women, and she is generally accepted by those around her, with only Kon, the protagonist from another world, initially reacting with shock. Her primary motivation is to protect the princess and enjoy life to the fullest. Within the story, she is a core member of the traveling party alongside Princess Ecarlate, Sainglain, and Kon. She shares a close, protective bond with Ecarlate, and works effectively with Sainglain as a fellow fighter. Her relationship with Kon evolves as he comes to respect and call her "nee-san." Mariandale undergoes development when she gains the ability to channel Alma Energy, granted to her by Almaflora near the end of the series, which further enhances her combat abilities. Before that, she already possessed notable physical strength, able to lift and swing large logs and fight on par with Sainglain. She is an expert marksman, wielding pistols with great accuracy, and is highly acrobatic and agile, capable of dodging rockets and leaping away from explosions. Her years of battlefield experience give her heightened situational awareness, making her difficult to ambush. She also has remarkable stamina, able to fight for hours without tiring and consume large amounts of alcohol without becoming drunk. Near the conclusion of the series, she undergoes a notable physical change by having Almaflora transfer her testicles to the antagonist Erecpyle.