Luchs, also known by the spelling Lux, is one of the three Saber Dolls, also referred to as Saber Marionettes, created by the dictator Faust to serve him. She is the counterpart to Cherry among the heroines of the series. Her name is a German word meaning lynx, and she is the last of the Saber Dolls to be introduced in the story.

Luchs has a mysterious and aloof personality, often maintaining a cool and distant demeanor. She is highly cunning and intelligent, serving as the strategist and intelligence specialist among Faust's forces. She can devise complex, devious, and subtle plans very quickly, and she is not above manipulating or deceiving even her fellow Saber Dolls if it benefits her objectives. She approaches situations with a meticulous and cautious mindset, striving to eliminate any chance of failure before committing to an action. Despite her generally cold and ruthless nature, she has been known to act in a silly or unexpectedly lighthearted manner on certain occasions. She also possesses a vivid imagination, prone to intense fantasies similar to those of Cherry, which sometimes lead to awkward or humorous situations.

Luchs's primary motivation is her unwavering devotion to Faust. She is deeply in love with him and will carry out any order with ruthless efficiency and perfectionism. Unlike another Saber Doll, Tiger, Luchs only knew Faust after he had become cruel and ambitious, and her emotional development reflected that environment, shaping her into a cold-hearted and ruthless fighter. She desires his approval and affection above all else.

In the story, Luchs initially serves as a primary antagonist, directly opposing Otaru Mamiya and his three marionettes, Lime, Cherry, and Bloodberry. She is the most calculating of Faust's subordinates, and her battles with Cherry often become stalemates of tactical analysis, with both using their advanced sensor systems to probe for weaknesses. Her role expands in later arcs, including the Mesopotamia arc, where she assists in the mission to rescue Lorelei due to her unique ability to access the ship's computer systems. In the OVA, she is placed under Otaru's care to learn about ordinary life and general knowledge, leading to further character development as she experiences a more domestic and less militant existence. In subsequent series, she remains loyal to Faust but also begins to carve out her own path, eventually working as a reporter.

Key relationships define her character arc. Her relationship with Faust is central, marked by absolute loyalty and deep affection. She interacts with Tiger and Panther as fellow Saber Dolls, but she is willing to outmaneuver them to gain Faust's favor. She serves as Cherry's direct counterpart and rival, and their encounters are characterized by mutual respect for each other's intellect. Her time living with Otaru and his marionettes leads to a gradual softening of her demeanor, though she retains her sharp, calculating edge.

Luchs has notable abilities that make her a formidable opponent. She possesses the same advanced sensor and battlefield analysis systems as Cherry, allowing her to scan environments, analyze objects, and detect weaknesses with precision. She is also highly skilled at manipulating technological equipment, including computers and spacecraft. In combat, she uses small, explosive throwing daggers or knives, which she can throw with perfect accuracy. She can throw multiple knives simultaneously and detonate them on impact. She has also demonstrated the ability to fire energy projectiles from her hands, though this is seen less frequently. Her strategic mind is perhaps her greatest weapon, as she can think through multiple attack scenarios in seconds and execute the one with the highest probability of success.