After returning to his human form, Tanjiro loses the ability to see from his right eye, the iris of which is now a dull pink-gray color and the pupil black rather than its original white.
After Doma's demise, Kanao wears Shinobu's hair pin instead of Kanae's, as the latter was destroyed during the fighting. Furthermore she loses visibility in her right eye due to unleashing the final form of Flower Breathing, even though the eye is unaffected visually.
Chapter 204 of the series reveals the extent of Tanjiro's injuries, and although he was able to survive the battle after seemingly coming close to death, he's far from 100 percent as he's completely lost the use of his left arm and can no longer see out of his right eye.
However, they were just barely able to kill Doma with young Kanao using a Flower Breathing technique that involved her eyesight, but doing so caused significant damage to her eyes. She's blind in her left eye and can barely see in the right.
Kanao Tsuyuri is the adoptive sister of Shinobu Kocho, whom she has been training under since she was a young child. Having trained under one of the Pillars of the Demon Slayer Corps, Kanao was the strongest of the group that survived the Final Selection, a group that included Tanjiro.
Tanjiro Is Strong, and Stronger than Zenitsu as he uses Sun Breathing.
In hopes of rectifying Kanao's problem, Kanae bequeathed the young girl with a coin which Kanao would flip to decide what to do when she was unsure of herself. She remained emotionally stunted for several years and expressed practically no desire to speak of.
Kanao never spoke before being adopted into the Demon Slayer Corps and continued to have difficulty speaking after officially joining the other demon slayers. To help with her indecisiveness and other struggles, Kanao often flips a coin she received as a gift.
Kanao is a dedicated demon slayer and a good friend to Tanjiro. She hardly ever speaks, even to Tanjiro. Instead, she flips coins to make her decisions for her, making her oddly similar to Two-Face from the Batman comics. She might have a few words for Tanjiro, though, with or without that coin.
The fuming rage that Tanjiro felt from seeing Daki destroy human lives helped him push past his limits while also making him bleed through his eyes in anger, resulting in his eye colors changing to bloodshot red.
Though he eventually avenges his family during the final battle, he loses his left arm and right eye in the process while being fatally wounded. Both are restored during Muzan's attempt to turn him into his successor by transforming him into a demon, though with the aid of his friends, he becomes human once again.
In episode 6 of Demon Slayer season 2, Nezuko entered a berserk state to protect her brother Tanjiro, causing her body to develop into that of an adult. She loses her gag, grows a single horn and gains vine-like patterns across her body.
After returning to his human form, Tanjiro loses the ability to see from his right eye, the iris of which is now a dull pink-gray color and the pupil black rather than its original white.
She recalls that when Kanae died, she was unable to cry, but no one judged her for it. Kanao remembers how Kanae had advised her to value her comrades, and wonders if she did so correctly this time, as she cries for Shinobu.
Tanjiro lost his eye!? Yes, literally at the beginning of the fight. Tanjirou losing an eye... I fully expect Nezuko to show up next time Tanjirou takes a hit with the fortress falling.
She was killed by Doma.
Kanae Kocho, the Flower Hashira, was Shinobu's elder sister and adoptive elder sister of Kanao Tsuyuri.
After the battle, Tanjiro returns home with his sister and friends. Later it is revealed that he married fellow slayer Kanao Tsuyuri.
The muzzle serves as a representation of Buddhist practices. First, it gags Nezuko, preventing her from speaking like a Buddhist monk's vow of silence, but it also is there to suppress her desire to eat humans. Through a Buddhist lens, Nezuko's muzzle is the symbol of a Buddhist monk.
Post-Transformation
Sensing their despair, Doma offered a chance to him and turned both Gyutaro and Daki into demons.
Kanao Tsuyuri, Shinobu's adoptive sister, holds the rank of Tsuchinoto, one rank higher than the aforementioned Slayers. As a Tsuguko, she is expected to succeed her Hashira sister in the future.
Although Inosuke possesses immense strength and endurance, he's no match for Zenitsu's insane speed and his Thunder Breathing.
Zenitsu is clearly on the same level as Hashira. If we compare him to Shinobu, his speed is far better, while she lacks quite a lot in raw power. There is a good chance that he could beat Shinobu if the two decide to fight.
With his master gone, Zenitsu can no longer learn the remaining five forms.