Kirara

is Sango's faithful nekomata companion and main method of transportation.

History
Kirara was originally the companion of Midoriko, the miko who created the Shikon no Tama, suggesting that she's far older than she seems which makes her the oldest member of Inuyasha's group. Sometime later, she became Shako's family companion and has been passed down through the line. She was inherited from Shako to Sango's father, who then gave Sango, Kirara, when Sango was still very young.

During the Story
When Kirara is first introduced, she was greeting Sango after Sango had come home from a mission. She is then seen playing with Sango right before Sango and the other Yōkai Taijiya go to Hitomi castle and are slain. She helps fight to protect the Demon Slayer village during the attack, ending up the only survivor. She was discovered by Myōga during this time and joined Inuyasha's group on their search for the Hitomi clan castle. During the search, she reunited with Sango, who ordered her to kill Naraku if he did anything suspicious.

After these events, Kirara travels with Inuyasha's group and acts as an ally and friend through the entire series. Kirara becomes fast friends with Shippō, often seen in his company when Sango isn't around. When someone is depressed, Kirara often allows them to rest on her for comfort.

When Kohaku is brought back to life by a jewel shard, Kirara is ordered to kill Naraku to break the spell on him; however, she ends up badly poisoned by biting his shoulder, which released miasma. She is later cured of the poison thanks to Jinenji's antidote.

In Kirara Come Home, it's shown that Kirara is, at times, abused by Inuyasha, Kagome and Miroku for their own selfish needs; Inuyasha accidentally burned some of her fur off while practicing the Wind Scar, Kagome used her for quick transport to the Bone Eater's Well while forgetting promised cat treats to return the favor, and Miroku used Kirara to stage demon attacks to meet women. Despite this, she appears to hold no grudge towards them and the group is in deep regret for their past actions.

Shown in Kohaku, Sango and Kirara: The Secret Flower Garden, Kirara has many fond memories of her time living with Sango and Kohaku in the Demon Slayers' village. She meets Kohaku during this time, and learns he's free of Naraku's spell. She hears Kohaku wishing that Sango could see the field of lilies near the village, so Kirara leads her there.

Three years after Naraku's defeat, Kirara joins Kohaku as he trains to become a demon slayer.

Personality
Since Kirara is a cat demon, she acts similar to regular cats: eating cat food, treats, fish, and playing with cat toys. She also has cat-like weaknesses too. Kirara is shown to be very intelligent as well as sentient. She's fiercely loyal to Sango but with time she shows loyalty to all members of the group.

Kirara demonstrates exceptional patience, often honoring the requests of the group and their various friends. For example, it is revealed that she allowed Inuyasha to practice the potentially lethal Kaze no Kizu attack on her leaving bald spots on her fur. In addition, she also helped Miroku impress village women and ward off the undesired advances of the older village women. Kagome admits to playing dress up with her, and using her to return to the modern age without the knowledge of the rest of the group.

Physical description
Kirara usually appears to be a small kitten-sized feline with red eyes, a marking on her forehead and two tails. However, she has two forms: one of a small kitten, and one of a large cat resembling a saber-toothed cat. In her full-sized demon form, flames emerge from her feet and tails and her abilities increase tenfold allowing her to battle even the strongest of demon opponents.

Powers & Abilities
Transformation: Kirara has the ability to transform from a small kitten to a huge cat that resembles a saber-toothed cat. Whether she is transforming into the huge cat or back into the little kitten, she is engulfed in flames and then they disappear, revealing which form she was changing into.
 * Flight: When Kirara is transformed into her huge cat form, she has the ability to fly. She is capable of carrying three grown adults at once, but it tires her out quickly.
 * Enhanced Strength: In her transformed state, Kirara is very strong where several times throughout the series she managed to overpower many other foes including larger demons.
 * Enhanced Speed: While transformed Kirara's speed is extremely heightened. She was able to keep up with Entei and even to Inuyasha's top speed.
 * Enhanced Durability: Kirara is very durable in this form where she managed to endure a practiced Kaze no Kizu from Inuyasha while he was practicing on her of her own free will and emerged fairly unscathed with only a part of her fur shaved off.
 * Enhanced Endurance: Kirara can fight continuous battles against many foes while in this form for a considerable amount of time before tiring out which in turn forces her to transform back into her small kitten form.

Allies/Traveling companions
Due to their long past, Sango and Kirara are very loyal to one another and care for each other greatly. It seems that when Sango first got Kirara they both seemed very happy, so they have had the most wonderful friendship. Kirara often tries comforting Sango when she's sad, offering the comfort of her fur to try easing Sango's pain. Since Miroku came into the picture, Kirara has become greatly fearful of Sango's anger.
 * Sango

Kirara helps Inuyasha fight his enemies and they often work together. Sometimes, she's acted like a "trusted steed," allowing Inuyasha to ride her into some fights, sword drawn. Inuyasha respects Kirara, knowing she is reliable.
 * Inuyasha

Kagome treated Kirara as her own, and sometimes Kirara helps Kagome fight against demons. Kirara often gets cat food and treats from the modern era as thanks from Kagome, which she enjoys greatly. However, she has been seen to be a victim of Kagome's dress-up games because of how cute her kitten form is.
 * Kagome Higurashi

Miroku doesn't seem to have much of a relationship with Kirara, although she does help him to get attention of local village girls in one episode, by pretending to attack a village; she even chases off old women interested in Miroku. She apparently doesn't hold a grudge towards him for using her. Kirara often carries Miroku on her back along with Sango.
 * Miroku

Kirara is particularly close to Shippō, who are often seen playing together. This is probably because of their connections as being demons. Kirara is often seen with Shippō on her back when the others aren't riding her; she is most likely protecting him. At times when Sango is frightening, Kirara and Shippō hold each other.
 * Shippō

Other
Having lived with Kohaku most of his life, Kirara is close to him as she is to Sango. However, their relationship is quite strained due to Kohaku being under Naraku's control most of the series. In an anime-only episode, Kirara meets Kohaku once he's broken free of Naraku's spell and fights demons alongside him in perfect combination. She honors Kohaku's desire to have Sango see a secret lily field, leading her there. Following the three year time skip, Kirara acts as Kohaku's partner in his quest to become a strong Demon Slayer.
 * Kohaku

Trivia

 * When Kirara enters water, the fire on her tail and legs do not go out.
 * In the anime, it is shown that Kirara has been in Sango and Kohaku's family for at least three generations, as she is seen with their grandfather and father.
 * In the anime, the story of Midoriko, it seems Kirara was her partner.
 * Kirara apparently has very impressive eyesight or senses. In episode 136, when Sango was invisible, Kirara was able to precisely jump onto Sango's shoulder and put the balls into her hands.
 * Kirara's voice actor as same as Sugar's from Urusei Yatsura, another series by Rumiko Takahashi.