Lyar von Ertiana is a 29-year-old German military officer holding the rank of Lieutenant, later promoted to Lieutenant Commander. She stands 168 cm tall with measurements of 94-59-88. Her special ability is cocktail making, and she harbors concern over reaching marriageable age without prospects, aiming to be married by 30. She commands the elite Seraphim unit and supervises cadets Misaki Kureha, Luxandra Frail, Suzanna Bluestein, and Kiri Marialate from her post at the remote base Watcher's Nest. Initially slated for promotion and transfer to command headquarters with the cadets as replacements, her promotion occurs during the Tragedy of Cherubim, yet she remains stationed at Watcher's Nest. She maintains deep suspicion toward Jean Luc LeBlanc, head of the research group Alchemy, believing he withholds critical knowledge about the extradimensional Ghoul threats. Her leadership blends stern discipline with fierce protectiveness toward subordinates, exhibiting a "Mama Bear" instinct particularly toward Misaki and reacting severely to threats against her team. Technically proficient, she built and programmed the android support unit Kotoko-01, sharing a "Cool Big Sis" relationship with it. Unauthorized tampering with Kotoko's programming triggers intense backlash from her. In subsequent operations, she leads missions across different timelines to combat Ghoul incursions, traveling to historical periods like feudal Japan (1594) and pre-World War II Japan (1936). During these missions, she wears a distinctive cape and pilots upgraded equipment. Her dedication focuses on containing Ghouls and protecting her team, though she expresses weariness over the temporal conflicts. She actively attempts to dissuade Misaki from altering history to save deceased comrades. Decades after the collapse of Watcher's Nest, she becomes the last survivor of the Kessler Project, commanding a long-duration space voyage. Reviewing logs reveals evidence of Misaki's survival, leading to a heartfelt reunion. She also undertakes visits to the families of fallen comrades, including Luxandra and Kiri, acknowledging their sacrifices.