Linel, officially designated Linel Synthesis Twenty-Eight, operates as a supporting character within the Alicization narrative and one of the youngest Integrity Knights alongside Fizel Synthesis Twenty-Nine.

She possesses pale light brown hair typically styled in two braids, with droopy eyebrows and eye corners contributing to a consistently meek facial expression. Her standard uniform matches Fizel's: ink-black with a green belt from which she carries short swords approximately thirty centimeters in length. Crafted from toxic Ruberyl steel, these blades possess paralyzing properties and feature reddish wooden grips.

Unlike most children who receive their Sacred Tasks at age ten, Linel and Fizel were assigned theirs at five. Their task involved participation in a brutal experiment orchestrated by Administrator, ruler of the Axiom Church. Alongside twenty-eight other children, they endured repeated lethal combat. Administrator employed resurrection arts to revive the deceased, a process frequently causing memory loss, personality alterations, or catastrophic physical deformities. To minimize resurrection failures, Linel and Fizel trained rigorously to kill each other efficiently with single, precise strikes to the heart or head. The experiment concluded only when they remained alive.

Desiring to become Integrity Knights but facing rejection from Chief Elder Chudelkin, Linel and Fizel killed the previous holders of the Synthesis Twenty-Eight and Twenty-Nine positions during a match. This lethal act demonstrated their capability and compelled Administrator to admit them into the Integrity Knight Order as apprentices.

During Alicization Rising, learning of intruders from the Dark Territory within the Central Cathedral, Linel and Fizel sought validation as full knights by devising a plan to eliminate Kirito and Eugeo. Posing as sister apprentices, they approached the intruders, appeared to poison them using their toxic blades, and transported them from the 29th to the 50th floor. During transport, they revealed their tragic background to the captives. Kirito, however, deduced their scheme and secretly counteracted the poison using a Sacred Art. Upon arrival, while Linel and Fizel argued with Integrity Knight Fanatio Synthesis Two, Kirito immobilized them using their own poisoned weapons. Paralyzed, they witnessed Kirito's subsequent battle against the guarding knights. After the conflict, Kirito destroyed their toxic blades, confiscated other suspicious items, and provided Eugeo with the antidote to cure them.

In the later War of Underworld conflict, Linel joined the Human Empire forces defending against the Dark Territory invasion. Her participation stemmed from a desire to understand the values and convictions driving Kirito and Eugeo to fight, seeking comprehension of true mental fortitude beyond her ingrained proficiency in killing.

A distinction of Linel and Fizel among the Integrity Knights is their retention of memories from their human lives. Unlike most knights—winners of the Four Empires Unity Tournament or criminals violating the Taboo Index who underwent memory alteration—they were never subjected to the illusion of descending from the Celestial World. Trivia notes reveal that in the original web novel version, this character was a male Integrity Knight named Ashin Synthesis Thirty-Eight.