Atsui in Naruto

During the Fourth Shinobi World War, Atsui and his sister were sent to the First Division of the Allied Shinobi Forces. Atsui and his sister helped Darui as he faced the reborn Gold and Silver Brothers. He was instantly attacked by multiple White Zetsu Army clones and destroyed them before turning to face the opposing Kinkaku and Ginkaku.

He and Samui are both struck by the Kokinjo, which causes the removal of their "souls" ( kotodama) from their physical forms. The siblings are subjected to a mixed curse and sealing method after having their individual word souls split by the Shichiseiken(Seven Star Sword) and absorbed by the Benihisago (Crimson Gourd).

If they speak the word they have used most frequently during their lives, they will be imprisoned for all time. Atsui said "hot" in response to Kinkaku's attack against Samui which led to his entrapment within the gourd. Darui assured Samui, who was also drawn into the gourd, that he would find a method to free them.

Later, Tobi took the gourd that contained Atsui and Samui in order to lock the chakra of the Nine-Tails that was housed within Ginkaku, who had also been absorbed into the gourd at that point. He and his sister were eventually liberated from the Benihisago by Darui following the end of the war.

Atsui has a somewhat hot-headed and passionate demeanour, which is seen even in battle, in sharp contrast to his older sister Samui. He loves to engage with his rivals head-on, which occasionally leaves him without any help. He acknowledges that he frequently uses the term "hot" (atsui) and that he has produced a significant amount of "hot-shot" catchphrases.

He is prone to emotional outbursts when upset and is known for his fiery personality. He is also willing to do anything to achieve victory at all costs, making him an unbridled character.

Atsui has green eyes and blond hair that is styled in an asymmetrical bowl cut to his neck. He usually wears a sleeveless variant of the Kumogakure uniform and the corresponding jacket for his village. Additionally, he wears shin guards, bandages on his forearms, and a tattoo of the character for "heat" (netsu) on his left shoulder.

Atsui, like many other Kumogakure shinobi, is an expert user of kenjutsu and uses a long, white-hilted katana as part of his primary combat technique. He has the ability to channel fire-based chakra into his sword, which gives him the power to instantly vaporise a significant number of opponents. He further demonstrated his ability to summon flames with each thrust of his sword.