Agni is a tall Indian man with dark, olive skin, slate-gray eyes, and short, stark white hair. Two long locks of his hair are adorned with beads.
Agni dons a plain turban and a green sherwani with a yellow and white sash-over churidar. He wears silver hoop earrings and a decorative bindi. He keeps his right hand and forearm wrapped in bandages and only unwraps them when calling on the power of his faith in his goddess Kali to accomplish difficult tasks.
Before he met Soma Asman Kadar, Agni had long hair that reached past his waist.
Agni is a kind, caring, and compassionate individual who works to the fullest of his capabilities to make others feel welcome, useful, and needed; he demonstrated this trait when he identified the Phantomhive servants' strengths and assigned them compatible tasks. Agni is exceptionally humble, and he frequently dismisses praise.
Additionally, Agni admires and adores Soma, whom he often calls his god, and will do anything to make him happy. Even when he appeared to betray Soma, he did so only to protect him and was deeply grieved by his own actions. He does his best to remedy any wrong he has committed, even at the insistence of others that he forgives himself.
When his name was Arshad, Agni and his family were part of a high caste of Brahmins, whom of which were reportedly able to serve the gods. As a child, he witnessed his father indulge in luxury and material items, which triggered his loss of faith in God. Taking after his father, he yielded to his desires, and he took advantage of his prestigious social class to commit sins on a daily basis. After hurting a lot of people, he was eventually called to pay for his crimes via an execution.
On the day of his ordered execution, Agni, who had lost all affection for the world as well as his faith in God, was prepared to die. However, Soma Asman Kadar arrived, having heard that Agni was very strong, and nominated Agni as his sparring partner. His attendants told Soma that his proposal was not allowed because Agni had already been scheduled to be executed. In response, Soma cut Agni's hair and declared that he was to be reborn with a new name and a new life. Agni accepted the offer because he felt that God existed in Soma.
Indian Butler Arc
Agni and Soma first encounter Ciel Phantomhive, Sebastian Michaelis, and Lau in East End, when a group of Indians attacked the latter group. Soma, initially, sides with the Indians, and he orders Agni to attack Sebastian. Agni complies, but Sebastian manages to avoid his blows although he comments that Agni moves very quickly. An Indian man enters the battle, trying to attack Sebastian from behind, but Agni unintentionally punches him, and he apologizes. Their fight resumes, and Agni deliberately strikes Sebastian's vital points (an advanced technique named marma adi). He notes that Sebastian's arm should be paralyzed and questions how he is still able to fight.
Agni and Soma soon learn that the Indians are the ones at fault as they have attacked the Englishmen for only destruction's sake, and by Soma's orders, Agni single-handedly defeats them. Later that evening, the two of them arrive at Ciel's London townhouse; they justify their residence by stating that they have saved them. Agni offers to prepare tea, and Ciel demands that they leave, but they refuse.
The following morning, Agni cheerfully wakes up Ciel, much to the latter's annoyance. He has also taken the liberty to prepare the food, wash the clothes, and tend the garden, and Sebastian is immensely impressed. At breakfast, Soma reveals that he and Agni are looking for a maidservant named Mina. Subsequently, they pray to the statue of the goddess Kali, and Agni explains her significance. When Soma learns that Ciel will not spend the day with him, he and Agni follow him around as Ciel does each of his lessons. At the fencing lesson, Ciel and Soma confront one another, but Agni interferes, out of fear of seeing Soma in danger, and he inadvertently injures Ciel's arm. Because of this, he and Sebastian duel. They end up being evenly matched, and and the fight ends in a draw.
However, this event puts Sebastian behind schedule, so he goes to take over Baldroy's cooking duties. Agni offers his assistance, and he is put in charge of making the berry sauce and cottage pie. Sebastian dismisses Baldroy as a nuisance, and Agni swiftly finds a task that Baldroy can help with (i.e. chopping the onions) and respectfully regards him as the "chef supervisor." After learning of Finnian's immense strength, he puts that to use by assigning him to smash the potatoes with a spoon. He prevents Mey-Rin from falling and advises her to retrieve plates from high places at an unhurried pace. Sebastian is surprised that Agni is able to let them be of use and commends his capability. Agni denies as such, and he tells Sebastian of his history and his old contemptible self that had nearly gotten him executed until Soma rescued him.
That evening, Agni and Soma go out to search for Mina and return to the townhouse late at night. However, Agni leaves a second time, this time to the residence of Harold West Jeb. Soma, Ciel, Sebastian, and Lau follow him there, and they learn he is working with Harold for an important matter that involves Mina. Soma bursts in and requests information, but Agni is forced to attack him on Harold's orders. Soon after, Ciel, Sebastian, Lau, and Soma flee the place.
Agni has actually joined a local curry fair to win Harold a Royal Warrant, for Mina to be returned to Soma. In the competitor's room, he is astonished when he learns Sebastian has also entered the curry fair. Agni says that he has a reason for which he cannot lose, and Sebastian counters that he has one as well.
During the curry fair, with his "Right Hand of God," Agni impresses the crowd as he prepares the curry. On the other hand, the spectators are disgusted when Sebastian adds chocolate into his curry. Agni, however, remarks that they are wrong and that chocolate is a perfectly viable ingredient that is able to draw out the fragrance and the bitterness while leaving a smooth consistency. He notes that he has always known Sebastian was not an ordinary person, but he is determined to win, and he includes a blue lobster in his curry.
While the judges announce their curries as equal in quality, and thus a tie, Queen Victoria declares Sebastian the winner. Nevertheless, she later consoles Agni, saying that he did not lose and that she enjoyed his dish as well. After the curry fair, Soma finds Mina, who in turn is hostile to him—Agni has learned of Mina's true nature beforehand and wished to hide it from Soma; to protect him, he performed under Harold's orders. Soma, however, apologizes to Mina, then approaches Agni and asks if they can stay together. Afterward, Agni thanks Sebastian and says they are good friends, much to Sebastian's surprise.
The next day, Agni readily helps out at the townhouse, and when he learns that the dinner guests are the investigators on the Anglo-Indian case from Scotland Yard, he tries to confess that he was the perpetrator behind the Anglo-Indian attacks; this causes Sebastian to behave oddly as he works to prevent Agni from doing so. After dinner, Ciel reprimands him for almost getting him in trouble, and Soma forbids him from confessing. Soma decides he would like to stay with Ciel so he can become a good man, and Agni and Soma are given the duty of maintaining his townhouse.
Ciel and Sebastian briefly stay at the London townhouse in order to get closer to investigate the Noah's Ark Circus. They depart for two days while they infiltrate the circus; when Ciel comes back sick, Agni and Soma prevent him and Sebastian from leaving. Agni is able to convince Sebastian that going against orders, when it is a matter of protecting his master's health, is part of a butler's duty. Sebastian and Agni allow themselves to be instructed by Soma while they take care of nursing Ciel back to health.
While Ciel rests, Agni carries an exhausted Soma out into the hall and talks with Sebastian. He apologizes for yelling at Sebastian and states that he is a better butler than himself. Soma then tries to get Agni to lip sync with him while he calls Sebastian mean and tells him he should fawn over Ciel because Ciel does not have any parents. He then flees from Sebastian, and Agni calls him kind.
Later, when Ciel and Sebastian returned to the Phantomhive Manor without telling Soma and Agni, they follow them to the manor. There, they meet Elizabeth Midford, and Soma reveals to her that Ciel had recently been ill, prompting her to question why Ciel never tells her anything.
Phantomhive Manor Murders Arc
Later, at Ciel's London townhouse, Agni walks in Soma's bedroom and sees Soma listlessly staring out the window at the rain. When Soma voices his concern for Ciel, Agni reassures him that Ciel is safe because he has Sebastian with him.
On one occasion, Soma and Agni have just returned to the townhouse after shopping for groceries. They encounter Snake, who Soma mistakenly thinks is a friend of Ciel, and sends him on a horse carriage to the Phantomhive Manor.
Some time afterward, at Sebastian's funeral, Agni assists in carrying Sebastian's coffin. After he is buried, Agni cries with the other servants of the Phantomhive household. Sebastian then rings a bell to signal that he is still alive, and Agni, grabbing a shovel, helps to unearth him. Agni, then, expresses his gratitude to God for the miracle.
Luxury Liner Arc
Agni and Soma have decided to celebrate the Easter holiday at the Phantomhive Manor. There, Nina Hopkins dresses up Agni, Soma, Ciel, and Edward Midford, out of respect for the tradition that they must wear new clothes and hats on Easter Day.
Subsequently, they all prepare to compete in an Easter Egg Hunt for Elizabeth Midford's special egg. Sebastian adds some egg tapping-inspired rules: everyone will be divided into teams of two; a partner will carry a raw egg in a ladle during the Egg Hunt; one can freely exchange the egg through the use of ladles; a team is disqualified if, for whatever reason, the raw egg breaks. They are then arranged into groups, and Agni is partnered with Soma.
Agni and Soma target Ciel and Sebastian. While Agni battles Sebastian, Soma rushes to break Ciel's egg. Ciel suddenly starts coughing, much to the surprise of Agni, Soma, and Sebastian. Ciel, then, takes advantage of Soma's lowered defenses to break his egg. Though their team is disqualified, both Agni and Soma hug Ciel out of relief that he is not actually ill. After the hunt, Agni and Soma join the rest of the participants in a feast set outdoors.
Public School Arc
One morning as Sebastian is assisting Ciel, Soma bursts into his bedroom, demanding to know why he has left school. Ciel replies that he's welcome to stay, but Soma responds that he learned everything they are teaching when he was a young child. Sebastian and Ciel are left speechless after hearing this. Agni also comes in, and Sebastian casually comments that he just saw him last at Weston College, secretly protecting Soma. Infuriated that Agni went against his orders, Soma loudly complains to an upset Agni. Ciel and Sebastian use this opportunity to leave. Ciel tells them they will be leaving the mansion in their capable hands. 
Emerald Witch Arc
Agni greets Ciel and Sebastian after they return from Germany to the townhouse. At dinner, Agni is about to give Sieglinde Sullivan seconds because she demands them, but Sebastian does not let him because he is training her to be proper.
Blue Cult Arc
At Ciel's townhouse, Agni and Soma walk to where Ciel, Sebastian, and Edward are, incidentally overhearing Sebastian singing a popular song. Agni apologizes for interrupting them and offers sandesh; Soma claims that Agni makes the best sandesh. Soma asks if the song Sebastian sang is "all the rage" in England because he hears it sung quite often by kids when he goes out to the market with Agni. Sebastian discloses to all of them his inference on the purpose of the song, which originated from Sphere Music Hall, as well as the information he learned from his conversation with a prostitute.
Later, Sebastian returns with an unconscious Elizabeth, whom was retrieved from Sphere Music Hall and is, then, placed in a bedroom on the third floor. Subsequently, Agni, thinking that Elizabeth must have woken up, goes to check up on her, but discovers that she has escaped. A panic-stricken Agni, then, rushes to Ciel, Sebastian, and Edward, and informs them of Elizabeth's disappearance. They go up to the bedroom and inspect it. The doorbell sounds, and Agni leaves to get the door. A multitude of children enter, and Agni and Soma distribute food to them, to Ciel's shock. Soma explains that it is his duty to help the commoners, and Agni is proud, commenting that Soma has become a respectable man. Agni, then, offers to be scolded by Ciel, but Ciel, having come to a realization, announces that he has figured something out; when Agni asks if he is upset, Ciel denies it and thanks them instead, to Agni's surprise and Soma's delight.
Later, Agni approaches Ciel and Sebastian. Upon receiving confirmation from Ciel that Funtom Music Hall has triggered the incident where Sphere Music Hall killed a person, Agni asks Ciel to stop involving Soma in dangerous matters, for, in his perspective, Soma has indirectly taken part in a murder. Ciel states that he will stop putting them both to use, and that he has never considered Soma a friend, to Agni's astonishment. He adds that he tends to use all the pawns he has at his disposal and that if Agni does not like that, he is free to leave. While passing him, Sebastian calls Agni the "very epitome of a butler."
At the townhouse, Agni tells Soma that he has matured as a person during his time spent in England, and the latter agrees. Agni, then, suggests that they return to Bengal, or even visit other countries. When Soma asks him if he is worried about Ciel, he admits that he is. Soma asserts while Ciel should be fine without him, he wishes to be "his Agni," to Agni's surprise. He says that he wants to be a strong man who can support someone else, just like how Agni was there for him and declares that he is still Ciel's friend, even if Ciel does not think so. When he asks if they can stay in England a while longer, Agni, who is moved by his words, gives his consent.
A carriage arrives, and Soma goes to answer the door, while Agni makes hot tea. Agni thinks to himself that all his worry was unnecessary and that he simply needs to protect Soma until Soma and Ciel can solidify their friendship. He discovers a partially burnt photograph of a younger Ciel at the hearth, as well as another picture, and decides to put the remnants back together and hold onto them until Ciel is grown up. On closer inspection of the remains, he becomes shocked. He, then, rushes over to Soma, who is with a visitor. A shot is fired from the visitor's gun.
The assailant shoots Soma's hand. Enraged, Agni lunges at the assailant, but the latter stabs his side. They continue fighting, with Agni stunned by the attacker's speed and strength. When the assailant aims for Soma again, Agni shields Soma, taking the bullet in his place. Agni, then, reflects on his friendship with Soma, calling Soma "his sun," as he drags Soma to safety, while the assailant knifes him. He pushes Soma into a room and holds the door shut. Soma begs him to open the door, but he stays put and tells him that he was happy being his butler, just as the assailant attacks him from behind. Agni gets stabbed multiple times, and dies on November 15, 1889 from the knife wounds.
- "Everybody is born with different abilities and purposes in life with our calling and life being guided by God. Us humans just have to abide by God's will, naturally and slowly, in order to complete what we have to do."
- "Even if it costs my life, I will do anything to protect the prince who gave me a new lease on life. I hope to fulfill his wishes in any way I can!"
- "The evening sun as seen from the banks of Ganges, the evening sun seen in England. It has the same beauty."
- (To Sebastian Michaelis) "As a fellow butler . . . no, as your friend, I'll say this: your master's body is your first priority. Even though it goes against orders, don't you think considering Master Ciel's condition, you should have stopped him? It's for my master to be bright and healthy that I would risk my life. Isn't that what you would call a butler's aesthetics?"
- "Prince Soma. When you saved me that day, I am certain it was on a whim. But ever since then, you have been the sun in my sky. You brighten and darken as is your wont, and play havoc with me as you walk down your own path. You have no idea of all the people you've saved by simply shining up in the heavens. That part of you is also very like the sun itself. Prince Soma. Only with you as my sun could my days begin, and the breeze blow life into my stagnant heart, and the stillness of night heal me. So I pray that your life never grows dim. As long as you keep shining brightly, I know there is no ice that will not melt before you."
- Agni shares his birthday, August 24, with Rian Stoker.
- His name, Agni, means a Hindu deity: he is the god of fire, who accepts sacrifices.
- Agni, most likely, belonged to the Iyer sub-caste of Brahmin as the surname "Iyer" refers to and is carried by those who are part of this caste.
Out of Universe
- According to the official Kuroshitsuji character popularity poll, Agni is the eighteenth most popular character in the series, with 93 votes.