Aoi Kanzaki

Aoi Kanzaki is a Demon Slayer, although she works as a helper at the Butterfly Mansion rather than taking to the front lines.

Appearance
Aoi has deep blue eyes that fade to a lighter blue at the bottom, along with white rectangular pupils, straight black hair with a parted fringe, and twin tails. She wears two blue butterfly clips to keep her twin tails in place.

Aoi wears the standard Demon Slayer uniform with the addition of a white nurse dress on top of it. Her uniform is tinted slightly blue. She is often seen with a frown.

Personality
As Aoi trained Tanjiro Kamado, Zenitsu Agatsuma, and Inosuke Hashibira, she is very tough on them and often pushes them to their limits. She has a firm personality, unlike her colleagues at the Butterfly Mansion. Aoi's personality is somewhat similar to that of the young Shinobu Kocho, volatile and open. She often appears angry, generally displaying how she feels very clearly. Despite her somewhat gruff demeanor, she is internally kind and caring, doing her best to help the hunters that come to the Mansion.

History.
At some point, Aoi's family was killed by Demons. As a result, she was taken in by the Butterfly Mansion, where she received breath training.

Aoi managed to survive the Final Selection, though she claims that it was through pure luck. She was too afraid to go into battle despite passing the Final Selection and as a result, decided to work at the Butterfly Mansion instead. She seems to undervalue her work, claiming that she isn't doing much compared to full-fledged hunters.

Although she cannot fight, she is well versed in medical knowledge and was presumably taught by Shinobu. She helps with the upkeep of the Mansion and cares for injured hunters.

Rehabilitation Training_Arc
Aoi first meets Tanjiro when she discovers him and the Kakushi talking to Kanao Tsuyuri in the garden. She brings them inside to the recovery beds, displaying clear frustration at the injured Zenitsu's constant wailing. She provides care for the trio throughout their stay.

During the training portion of their recovery, she explains the general ways they will be trained, including massage, reflex training, and tag games. Aoi and Kanao both play reflex and tag games. Aoi is quickly beaten by Zenitsu, who refuses to splash the medicinal water on her. She is still displeased with him, as she had heard his rant about how wonderful it would be to train with girls since he gets to touch them. He also beats her in tag, but she punches him when he gets too touchy.

Aoi is also beaten by Inosuke in the games, and later by Tanjiro. She becomes annoyed when Inosuke and Zenitsu stop coming to training.

When the trio departs, she tells Tanjiro that she enjoyed sharing her time with him, and wishes him good luck. Tanjiro responds by thanking her for taking care of him, but she deflects this by saying it wasn't much since she can't fight like others. Tanjiro tells her that being unable to fight has nothing to do with it and that since she helped him, he'll carry her feelings into battle as well. Aoi seems surprised by this response, but not unhappy with it.

Abilities

 * Medical Knowledge: After training under Shinobu Kocho, Aoi can concoct most of the more simple medicines.
 * Above Average Strength: While Aoi is weaker than most of her fellow Demon Slayers, she is stronger than the average person, having gone through training under Shinobu and passing the Final Selection.

Swordsmanship
Water Breathing: Aoi was a user of the Water Breathing when she took Final Selection.

Despite her surviving Final Selection, she believed it was nothing but pure luck and decided to stop training with the Water Breathing and instead helped other Demon Slayers within the Butterfly Mansion.

Tanjiro Kamado
Aoi and Tanjiro seem to have formed a friendship. Tanjiro respects Aoi for her help and cares while he, Inosuke, and Zenitsu resided at the Mansion. He also thanks her for her work and assistance, which she seems to appreciate.

Kanao Tsuyuri
How close they are is somewhat uncertain, but the two get along and seem to have a somewhat sisterly relationship.

Shinobu Kocho
Shinobu is Aoi's mentor in the field of medicine and likely oversaw some or all of her demon hunter training as well. Aoi thinks highly of Shinobu, like all the other butterfly girls. Shinobu cares for Aoi and feels sympathy for how her family was killed by demons.

Inosuke Hashibira
They met each other, for the first time, at the Butterfly Mansion. In the beginning, he struggles to beat Aoi in all of the tasks due to not having a strong will. Later on, he is finally able to adapt and beat her. In comparison with Zenitsu and Tanjiro, he was harsher against her.

Trivia

 * Aoi's name, Aoi (アオイ) can have different meanings depending on the kanji used. For example, her name can translate to 'hollyhock' (葵) or 'blue' (青い).
 * However, her name is spelled with three katakana characters, so the meaning is currently unclear.
 * Aoi appears to have low self esteem, as seen where she disregards her survival of Final Selection.
 * Aoi ranked 24th in the first character popularity poll with 103 votes.