Saber, originally Artoria Pendragon, reigned as Britain's legendary King Arthur. Raised secretly as a girl despite historical depictions of a male monarch, she became king by wrenching the sword Caliburn from the stone, halting her physical aging. Her rule united Britain and led the Knights of the Round Table through countless battles. Betrayal by her sister Morgan le Fay and rebellion by her homunculus offspring Mordred culminated in the fatal Battle of Camlann. Mortally wounded, she forged a pact to become a Heroic Spirit, seeking to undo her kingdom's fall. As a Holy Grail War Servant, she typically manifests in the Saber class, possessing exceptional combat skills, high magic resistance, and mastery of swordsmanship. Her primary Noble Phantasm is Excalibur, a sword embodying humanity's hopes, often shrouded by the wind barrier Invisible Air. In the Fifth Holy Grail War, Shirou Emiya initially summoned her. Within the Heaven's Feel route's *lost butterfly* events, the corrupted Holy Grail energy manifestation known as the Shadow consumed Saber, transforming her into Saber Alter. This corrupted version retains Saber's core identity but displays inverted traits: darkened armor, pale skin, and eyes shifting from green to gold. Her personality becomes emotionally detached, ruthless, and tyrannical, though her fundamental ideals and duty persist beneath the corruption. The transformation amplifies latent self-doubts and negative psyche aspects, resulting in a colder demeanor. In *lost butterfly*, Saber Alter serves Sakura Matou, now the corrupted Holy Grail's vessel. Her most notable action involves confronting the Shadow-controlled Berserker, Illyasviel von Einzbern's Servant. During an extended battle, Saber Alter overwhelms Berserker, exploiting her corruption-granted enhanced strength and endurance. This confrontation highlights her heightened power compared to her standard form and emphasizes her role as the Shadow's weapon rather than an independent actor. After defeating Berserker, she departs without further engagement. Saber Alter's existence is intrinsically linked to the Shadow's influence and Sakura's transformation. The corruption distorts her methods, endorsing tyranny and absolute strength to achieve outcomes, without fundamentally altering her goals. She displays apathy toward the fates of Shirou, Rin, or Sakura, though a faint connection to Sakura's despair is noted. Physiologically, the corruption affects her beyond mentality, increasing her Magic Core's output and altering preferences like rejecting refined foods.