Demon Slayer fans saw one of the most heart-wrenching sacrifices of Kanao Tsuyuri during the series' final battles. The young swordswoman's journey from a traumatized child to a challenging warrior took a devastating turn that left viewers doubting the cost of her ultimate technique.
Kanao Tsuyuri went blind in one eye due to using Flower Breathing's Final Form: Equinoctial Vermilion Eye (also known as Scarlet Spider Lily Eyes) twice. This move compels the user's visual perception past human limits, allowing them to see the world in slow motion during battle. Nevertheless, the technique comes with an extreme price. The extreme strain can cause eye blood vessels to burst, resulting in irreversible damage to vision.
While battling Doma, the Upper Rank Two demon, Kanao was thrust into a desperate and chaotic struggle. The demon had already claimed the lives of her adoptive sisters, Kanae and Shinobu Kocho. Fueled by anguish and resolve, she made the utmost sacrifice to defeat this powerful enemy.

Demon Slayer's depiction of Kanao's battle showcases the vicious reality of demon hunting. Her improved vision ability, which normally permitted her to foresee enemy movements by following muscle shifts and eye movements, became both her greatest weapon and her downfall.
The Final Form technique essentially overclocks the user's visual processing system. By maximizing kinetic vision, warriors can perceive attacks in extreme slow motion. This gives them unprecedented reaction time and accuracy in combat situations.
Yet, the human eye is not designed to handle such drastic strain. The intense pressure overwhelms the blood vessels, causing them to rupture and inflict lasting harm on the retina. In Demon Slayer, this limitation describes the harsh reality that every power comes with consequences.
Kanao’s Sacrifice for Love in Demon Slayer

The most tragic aspect of Kanao's blindness wasn't during her fight with Doma but rather her final use of the technique to save Tanjiro. When Tanjiro transformed into a demon after defeating Muzan, Kanao made another heartbreaking choice. She sacrificed her remaining good eye to inject him with the demon-to-human conversion serum.
This moment in Demon Slayer perfectly encapsulates Kanao's character development. The girl who once couldn't make decisions without flipping a coin now made the most selfless choice possible. She gave up her sight to save the person she loved most.
Kanao's visual impairment operates as strong symbolism throughout Demon Slayer. She sold her exceptional sight for the ability to truly "see" what counted most—saving those she cared about. Though her eyesight was failing, Kanao continued to stand strong with the other demon slayers in battle.

Despite her weakened vision, Kanao held her own and fought effectively in the final clashes of the series. Her preparation and automatic responses enabled her to adjust to her fresh restrictions.
Her tenacity motivated both characters and admirers equally. Kanao's tale proves that champions aren't determined by their bodily perfection but by their readiness to sacrifice for others. This lesson echoes powerfully throughout the series' narrative.
By the conclusion of Demon Slayer, Kanao Tsuyuri had lost full vision in one eye and had limited sight in the other. Her sacrifice signifies the show's primary notions of affection, grief, and the cost of defending others. Through her narrative, viewers discovered that authentic perception originates from the soul, not the eyes.