Linel, designated Linel Synthesis Twenty-Eight, serves as a supporting character in the Alicization arc. Her appearance features pale light brown hair styled in two braids, droopy eyebrows, and downturned eye corners creating a meek expression. She wears an ink-black uniform identical to her partner Fizel's, complete with a green belt and short swords resembling thirty-centimeter daggers. These blades possess reddish wooden grips and are coated with paralyzing poison derived from Ruberyl steel.

Unlike most Underworld children receiving their Sacred Task at age ten, Linel and Fizel were assigned theirs at five. Administrator subjected them and twenty-eight other children to a brutal experiment forcing them to kill each other repeatedly. Administrator resurrected the deceased to continue the trials, though side effects caused memory loss, personality alterations, and some returning as non-functional "lumps of meat." To reduce resurrection failures, Linel and Fizel trained to kill each other cleanly with single strikes to the heart or head. When only they remained, Administrator abandoned the experiment. Both chose to become Integrity Knights, but Chief Elder Chudelkin denied their request. To prove their capability, they killed the previous holders of the Synthesis Twenty-Eight and Twenty-Nine positions during a match, compelling Administrator to accept them as apprentices.

Learning of intruders from the Dark Territory at the Axiom Church, Linel and Fizel sought validation as full Integrity Knights by devising a plan to eliminate Kirito and Eugeo. Posing as "sister apprentices," they lured the intruders into range and paralyzed them with their poisoned blades. Transporting the immobilized pair to the 50th floor, they recounted their tragic background during the journey. Upon arrival, they presented the captives to the guarding Integrity Knights and argued with Fanatio Synthesis Two. However, Kirito anticipated their strategy, having secretly chanted a poison-countering Sacred Art. He disarmed and paralyzed Linel and Fizel with their own weapons, leaving them incapacitated during his subsequent battle. After defeating the knights, Kirito provided the antidote to Eugeo to cure the girls, destroyed their toxic blades, and confiscated other suspicious items.

Following the defeat of Administrator and Chudelkin, Linel joined the Human Guardian Army to participate in the defense against the Dark Territory's invasion. She sought to understand the ideals driving Kirito and Eugeo's actions and discover the meaning of true mental fortitude.