Tomioka Giyu

Giyu is a man of strong equanimity, always wearing a calm and stern expression on his face. Having a stoic personality, and possessing a strong sense of justice and responsibility, he has no tolerance towards those who don't know their own limitations as well as those throwing 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.[10] Even so, Giyu violated the Demon Slayer Corps' code of conduct to protect Nezuko during Shinobu's attempt to eliminate her. This implies that he doesn't completely despise demons as some other Hashira do. Because he is willing to spare a demon if they don't kill and eat humans, he proves more pragmatic and impartial in dealing with demons as he does not allow his judgement to be clouded by hatred.

Due to his aloof personality, Giyu is not close to his fellow Hashira. While some are on even terms (but are emotionally distant) with 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, the Insect Hashira remained on fair terms with him afterwards. In the end, after defeating Muzan Kibutsuji, Giyu ended up developing a closer friendship with Tengen Uzui and Sanemi, his former "rival".

He is of very few words and lacks skill while interacting with others, choosing to observe from a distance.[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 can also be quite sardonic as shown when he frankly berates Inosuke Hashibira for mistaking Father as a member of the Twelve Kizuki, and he also sarcastically insulted Sanemi when the Wind Hashira made a remark about how simple he thought achieving a Demon Slayer Mark was. Giyu's quiet behavior can become a detriment to his reputation, as he does not explain his emotional feelings with his colleagues. This flaw was demonstrated when he denied his fellow Hashira an explaination as to why he refused to participate in Hashira Training; he continued to be uncooperative even after angering Sanemi and Obanai, and frustrating Shinobu.Beneath his seemingly aloof nature, Giyu suffers from an inferiority complex which he developed since his participation in Final Selection. This self-doubt caused him to initially refuse to participate in Hashira Training, showing through his words "I am not like the rest of [the Hashira]". This becomes so severe towards the beginning of the training arc that he contemplated abandoning his position as the Water Hashira. Ultimately, it took Tanjiro to help 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] The feeling of survivor's guilt struck Giyu yet again when Tanjiro appeared to die after the fight against Muzan. In that scene, Giyu shed tears as he admitted how he was always the one who was saved.

Despite his unfeeling attitude, Giyu is shown to be protective towards those he 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 demeanor when those he cares about are in danger, as seen when he is infuriated by Akaza's attempt to kill Tanjiro.[14]

Despite this, Giyu will not let his personal relationships get in the way of his duty. When Tanjiro, the person on the battlefield closest to Giyu, began his assault as a demon, Giyu was the first to announce that they needed to take him down. Following the death of Muzan Kibutsuji and the eradication of demons, Giyu was able to embrace his happier side, shown by his smiles towards the Kamado siblings and even Sanemi.In his childhood while training under Sakonji Urokodaki, Giyu is shown to have a much more cheery disposition, even considering that he had already lost one person in his life, his 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 entered a depressive episode. By his own commentary, he admitted 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 wanted to following the death of his friend. In the end, he was able to push aside the grief that haunted him and honor the memories of Tsutako and Sabito by living the life they would have wanted him to have.
Here is the English version with a good balance of detail and clarity:

Giyu Tomioka — Profile and Abilities
Giyu Tomioka is a main character in Demon Slayer: Kimetsu no Yaiba. As the Water Hashira of the Demon Slayer Corps, he is one of the most powerful and highly skilled swordsmen of his generation. Beyond his raw strength, Giyu is a perceptive teammate who can instantly read a battle and coordinate with allies.

Key Combat Achievements
Early Display of Power: Outclassed Tanjiro and Nezuko early on, effortlessly incapacitating both siblings in a single strike. Later, he easily defeated the transformed Father Spider Demon and Lower Rank Five, Rui—foes that had pushed Tanjiro and Inosuke to their absolute limits.

Peer-Level Sparring: Fought to a draw in a sparring match against fellow Hashira, Sanemi Shinazugawa.

Battle Against Akaza: Held his ground against Upper Rank Three, Akaza. Impressed by Giyu’s mastery, Akaza praised him as the most skilled Water Hashira he had encountered in fifty years and offered to turn him into a demon—an offer reserved only for the most formidable opponents.

The Final Battle: Played a pivotal role in holding off the Demon King, Muzan Kibutsuji. When Tanjiro was temporarily transformed into a demon, Giyu fought him off long enough to allow him to be restored to human form.

Core Traits and Combat Skills
Tactical Intellect: Exceptionally observant, composed, and analytical mid-battle. He quickly adapts to high-speed attacks, anticipates enemy strategies, and demonstrates extreme survival instincts—such as heating his own blade to cauterize heavy bleeding after his fight with Akaza.

Indomitable Will & Endurance: Pushes through severe, life-threatening injuries. Even after losing an arm, he remained on the frontline and continued fighting through sheer willpower.

Immense Speed & Strength: Capable of blinding movement and reflexes—easily outpacing fast fighters like Shinobu Kocho. His physical force allows him to sever dense demon threads and cut through high-durability opponents with ease.

Special Powers and Techniques
Demon Slayer Mark: Awakened on his left cheek during his clash with Akaza (appearing as a fluid, water-like design). It drastically boosts his speed, precision, and overall endurance.

Bright Red Nichirin Sword: By forcefully clashing blades with Sanemi during the battle against Muzan, Giyu temporarily turned his sword bright red, halting the Demon King's rapid regeneration.

Water Breathing (Mizu no Kokyū): Trained under the former Water Hashira, Sakonji Urokodaki. Giyu has completely mastered this style and created an entirely original technique within it: Eleventh Form: Dead Calm (Nagi).