Akatsuki is a twenty-year-old university student whose real name is Shizuka Hanekura. In the real world, she practices kendo but has an extremely petite stature that often causes others to mistake her for a middle school student, a source of deep personal insecurity. Before the Catastrophe trapped players inside the game world of Elder Tale, she chose a tall, male avatar to escape preconceptions tied to her appearance, communicating only through text to maintain a silent assassin persona. When the Catastrophe occurs, she finds herself inhabiting this male body and experiences significant distress. The strategist Shiroe provides her with a rare Appearance Reset Potion, allowing her to change her avatar to a female form that reflects her true self. Profoundly grateful, she pledges herself as his loyal servant, addressing him as Master and styling herself as his ninja bodyguard.

Akatsuki is reserved, serious, and speaks very little, uncomfortable in large social situations. She has a low tolerance for perverse behavior and frequently punishes her comrade Naotsugu with a knee strike for his inappropriate comments. Her sensitivity about her height remains a defining trait, as she craves recognition for her competence rather than being treated as a mascot. Her feelings for Shiroe evolve from gratitude and fealty into genuine romantic love, though she struggles to express these emotions directly and feels insecure compared to his more experienced former teammates.

As a founding member of the guild Log Horizon, Akatsuki serves as a skilled combatant and stealth operative. Her main class is Assassin and her subclass is Tracker, making her an expert in reconnaissance and high-damage strikes from the shadows. Her real-world kendo training gives her an advantage in physical sword combat. Her signature weapon eventually becomes the legendary blade Haganemushi Tatara, which can degrade the durability of any weapon it strikes. Her most distinctive ability is an overskill called Shadow Lurk, which allows her to create tangible clones of herself that can attack and swap positions with the original, making her a formidable and elusive opponent.

Throughout her journey, Akatsuki overcomes deep-seated self-doubt and her habits as a solo player. A significant turning point occurs during a serial killer incident in Akihabara, where she confronts her feelings of inadequacy, evolves her skills, and gains confidence. She learns to see her small stature not as a hindrance but as an asset for a master of stealth. Her key relationships include her devoted bond with Shiroe, a bickering yet trusting camaraderie with Naotsugu, and deep respect for the swashbuckling Nyanta.