Seryu Ubiquitous was a member of the Jaegers, formerly a member of the Imperial Police. She was a young girl with a strong (and twisted) sense of justice. She was the owner of the Teigu, "Hekatonkheires" until her death, which also resulted in the destruction of the Teigu. Seryu was a young woman with auburn hair and amber eyes. During her first appearance, she wore her hair in a long ponytail that almost reached the ground, but it was shortened to shoulder-length after becoming a member of the Jaegers. She was typically seen in a military uniform in favor of dresses and casual wear, and was frequently attired in upper-body armor. Her arms are metallic in place of flesh due to the heavy body modifications performed upon her by Dr. Stylish. When not in her military uniform, she was typically seen wearing a green coat or dress, sometimes with a white skirt underneath.

When in battle and speaking about justice, her face can distort into a warped and demented smile, which has become her trademark over time. Although Seryu initially appeared as a kind and compassionate person, she is actually a ruthless, psychotic, sadistic and unstable person who seems to enjoy killing to a high extent those of whom she considered to be evil, almost as if it was a hobby.

She has a strong fixation upon "justice", originating from her father's service in the Imperial Army and subsequent death. She also highly respected Ogre the Demon, her superior and teacher, and was heavily anguished by his death as well. Her opinion of justice is blunt, as she believes Night Raid is evil for their actions as assassins, but believes killing in service to justice is always right, which ultimately makes her opinion of murder similar to that of Tatsumi and Chelsea's, if not completely the same. Seryu had a twisted sense of right and wrong, bordering on a completely black and white view of the world: seeing the authority of the immensely-corrupt Empire as absolutely right, and its enemies as pure evil. She was fully committed to her duties and relished