Luke Harden, whose full name is Lukather Harden, is a central character in the anime Garo: Vanishing Line. He is both a Makai Knight and a Makai Alchemist, trained in alchemy by his mother, Adelaide, and in knightly combat by his father, Christopher. After his father became corrupted and murdered his mother, Luke abandoned his role as a Makai Knight and focused on his work as an alchemist, wielding firearms and magical ammunition rather than a traditional blade.

In terms of personality, Luke is calm, reserved, and speaks very little. He maintains a serious and principled demeanor, often clashing with the more reckless and human-friendly approach of the main protagonist, Sword. Luke disapproves of Sword's habit of involving ordinary humans in Makai affairs and his lack of concern for secrecy. Luke is deeply traumatized by his mother's death, which has made him emotionally guarded and rigid in his adherence to the rules of the Makai. Despite his cold exterior, he has a strong sense of justice and is fiercely loyal to those he comes to trust.

Luke's primary motivation is to protect the innocent from Horrors while upholding the strict code of the Makai. His personal trauma drives him to avoid close relationships with humans, but he is also driven by unresolved anger and grief toward his father. As the story progresses, the reappearance of his father forces Luke to confront his past, leading him to gradually rethink his isolationist attitude and become more open to cooperation.

Luke serves as a skilled ally in the fight against the Horrors and the mysterious organization El Dorado. He initially works alone in Russell City, but after encountering Sword and the young orphan Sophie, he becomes a key member of their team. His role often involves providing long-range support, cleaning up evidence of Horror encounters, and using his alchemical knowledge to counter supernatural threats. He also serves as a foil to Sword, representing a more cautious and by-the-book approach to their shared mission.

His key relationships include his sister Gina, who is also a Makai Alchemist and serves as a grounding presence; Sophie, toward whom he grows protective; and Sword, whose carefree methods frustrate him but ultimately earn his respect. He also interacts with the retired Makai Priest Fei Long and his granddaughter Mei Fang, who help him begin to trust others.

Luke undergoes significant development over the course of the series. The trauma of his mother's murder and his father's betrayal had made him emotionally closed off and overly reliant on rules. When his father reappears as an enemy, Luke is forced to face his pain and insecurities. Through his encounters with Sword and Sophie, he learns that isolation and rigid principle are not the only ways to fight evil. He starts to let down his guard, forming genuine bonds with his companions and reconsidering his stance on involving humans.

Among his notable abilities, Luke is a master marksman, using a variety of firearms including an anti-materiel sniper rifle and dual pistols. His ammunition is imbued with magical properties; one notable type creates rain that erases the memories of humans who witness Horror attacks. He also employs a bracelet capable of tracking Horrors, and he uses alchemical knowledge to create barriers and other effects. Despite initially abandoning his knightly training, he retains the ability to summon a Makai armor when necessary, though he prefers to rely on firearms and alchemy. Luke is also proficient with technology, using a motorcycle as his primary mode of transport.