Tomioka "Water Hashira/Pillar" Giyu(u)

Giyu is a fairly tall young man of a lean muscular stature and pale complexion, who is almost always seen wearing a stoic expression. He has choppy raven-black hair of uneven lengths, with jaw length side-bangs, a low messy ponytail at the base of his neck, and bangs falling over his eyes in a choppy fringe. His eyes are sharp and moderately large, having irises a lapis blue color, and their pupils a navy blue, sometimes having his irises completely opaque and empty, just in lapis blue color, and are framed by thin eyebrows.

Giyu wears a black standard Demon Slayer uniform, tinted in charcoal color in the anime, consisting on a button-up jacket with golden buttons, stand collar and long sleeves, a white belt, and a tattsuke hakama pants wrapped by white kyahan, having a pair of white zōri with dark blue straps and tabi socks underneath being the same color as his uniform. Over this, Giyu wears a haori that's split down the middle into two different halves: the right one in a carmine color, and the left one in a geometrically patterned rhombi prints, in green, dark green, orange, and yellow. These haori were later noted to have belonged to his late older sister, Tsutako Tomioka, and his deceased friend Sabito.

Giyu is a man of strong equanimity, always wearing a calm and stern expression on his face. Having a stoic personality, and possessing a very strong sense of justice and responsibility, he had no tolerance towards those who don't know their own limitations and throw away their lives.[9] Despite letting Nezuko Kamado live due to Tanjiro Kamado's determination, he shows zero hesitation when killing other demons and has no respect or mercy towards them like most Demon Slayers.[10] Even so, Giyu violated the Demon Slayer Corps' code of conduct without hesitation to protect Nezuko during Shinobu's attempt to kill her. This implies that he doesn't completely despise demons as some other Hashira do, and is willing to make an exception for a demon by letting them live if they don't kill and eat humans. This shows that he is more pragmatic and impartial in dealing with demons rather letting his hatred cloud his judgement.

Due to his aloof personality, Giyu is not close to his fellow Hashira. While some are on even terms but emotionally distant from him, others view him with apathy, or even disdain; Sanemi Shinazugawa and Obanai Iguro were particularly contemptuous of the Water Hashira due to unfoundedly misreading his aloofness as arrogance. Giyu also expressed surprise when Shinobu Kocho mentioned that he is hated by the others; despite this, he remains on good terms with her, with both having a great deal of history together. In the end, after defeating Muzan Kibutsuji, he ended up developing a closer friendship with both Tengen Uzui, and his former rival Sanemi.

He is of very few words and isn't very good interacting with others, choosing to observe from a distance quietly.[11] He even goes out of his way to tell Akaza that he hates talking and wants to keep his name to himself, as he thinks names are not meant to be shared, especially to demons. He could also be quite sardonic as shown when he frankly berates Inosuke Hashibira for mistaking Father as a member of the Twelve Kizuki, and sarcastically insulting Sanemi for complaining that the way to achieve a Demon Slayer Mark was simple. However his quiet behavior could become a detriment to Giyu's reputation, as the Water Hashira did not explain his deeper emotional feelings with his colleagues, and uncooperatively declined explaining his reasoning to not particpate in Hashira Training, angering Sanemi and Obanai, and even causing his closest ally Shinobu to ask Giyu to explain himself.

Beneath his seemingly unemotional and aloof attitude, Giyu suffers from an inferiority complex which he developed since his participation in Final Selection. This self-doubt in himself caused him to initially refuse to participate in Hashira Training due to in his words "not being like [the Hashira]", and it reached the point where he contemplates abandoning his position as the Water Hashira until Tanjiro helps him realize that instead of acting on his survivor's guilt, he should cherish his life and live on for the people who sacrificed their lives for him.[12] This feeling of survivor's guilt strikes again when he believes Tanjiro has died after the fight against Muzan. Giyu, while he sheds tears, admits how he is always the one who is saved.

Despite his stoic nature, Giyu is shown to be protective and caring towards those he is close to and considers his friends. This is first shown when he puts his life on the line for Tanjiro and Nezuko by vowing to commit seppuku if the latter were ever to eat a human.[13] Giyu has been shown to lose his composure and usual stoic demeanor when those he cares about are in danger, as seen when he is greatly angered by Akaza's attempt to kill Tanjiro and visibly shocked when he hears the news of Shinobu's death.[14] This is further shown in the fact that he still wears half of Sabito, his late best friend's, and his older sister's haori as a memento of them. However, Giyu appears to be particular in who he shows emotions for, as he doesn't appear to react at all when informed of the passing of Genya Shinazugawa and Muichiro Tokito.

Despite this, Giyu will not let his personal relationships get in the way of his duty. When Tanjiro begins his assault as a demon, Giyu is the first to announce that they need to take him down, despite his brotherly-type relationship with Tanjiro. Following the death of Muzan Kibutsuji and the eradication of demons for good, it is clear that Giyu has been able to embrace his happier side, shown by his smiles towards the Kamado siblings and even Sanemi, which shows how much their combative relationship has slowly developed into one of mutual respect.

In his childhood while training under Sakonji Urokodaki, Giyu is shown to have a much more cheery disposition, even after the tragic loss of sister. This can be attributed to his friendship with fellow trainee Sabito, as the two were very happy in each other’s company. After Sabito’s death during Final Selection, Giyu flies into a depressive episode. By Giyu’s own commentary, he admits to wanting to stifle this memory to prevent his tears, implying that a reason for his emotionless persona was to prevent himself from grieving that way that he did following the death of his friend.