Ais Wallenstein is a first-class adventurer and executive member of the Loki Familia in Orario, widely known by her epithet the Sword Princess. She has long golden-blonde hair, gold eyes, and a slender build, typically wearing white and black battle cloth with armor pieces, though she favors a simple white dress when above ground. As a child, her parents—the hero Albert and the wind spirit Aria—were killed by the One Eyed Black Dragon, an event that instilled in her a deep hatred for monsters and an all-consuming quest for vengeance. She joined the Loki Familia at age seven and has since become a Level 6 adventurer, achieving record-leveling speed including reaching Level 2 within her first year. Quiet and reserved, Ais struggles to express her emotions verbally, often coming across as mysterious or aloof, yet she possesses a childlike naivety and does not look down on weaker adventurers. She has a notable fear of water and cannot swim due to a traumatic childhood punishment from her mentor Riveria. Her combat abilities include exceptional speed and strength, the unbreakable sword Desperate, the wind enchantment magic Ariel, and the unique skill Avenger, which boosts her attack power against monsters in proportion to her hatred. Her worldview is challenged when she encounters the Xenos, sentient monsters, and after witnessing the monster girl Wiene protect Bell Cranel, she resolves to judge each being individually rather than exterminating all monsters on sight. Her relationship with Bell Cranel begins when she saves him from a Minotaur; intrigued by his rapid growth, she secretly trains him, and their interactions evoke rare displays of happiness and growing protective feelings. Within her familia, Riveria serves as a maternal figure, while her goddess Loki often teases her with perverse antics.