Later

Misaka 10032's cat is a recurring black cat that is owned by Misaka 10032. Originally only appearing in the third volume of Toaru Majutsu no Index, the cat receives expanded appearances in the Toaru Kagaku no Railgun manga, where its significance to the Misaka clones is much more prominent.

Appearance
Like Sphynx, the cat is only a mere kitten. The cat sports a black fur coat.

Sisters Arc
The black cat first appears on August 15, stuck upon a tree to which Misaka 9982 happens to chance upon. As Misaka Mikoto arrives after sensing her sister. Misaka 9982 manages to convince her to help her get the black cat out of the tree, and ignore her demands for answers on to who she is. The cat falls but Misaka 9982 manages to catch it with her skirt, much to Mikoto's complaints as she is unnerved that a clone of hers actually exists. Misaka 9982 and Mikoto try to pet it, but it is too sensitive to the electromagnetive fields that the both of them emit, as they are electromasters. Mikoto, however, scares the cat after she yells at her predicament, remembering that she has a clone.

At some point in time, Misaka 10032 manages to find the cat, and on August 20, Kamijou Touma finds her with it, trying to feed it, but to no avail, due to the electromagnetic field that she emits. Misaka 10032 later forces Touma to carry the cat, and while talking, Touma asks what she would like to call the black cat since it is hers. Misaka 10032 tries to name the cat, Dog, Tokugawa Ieyasu, and even Schrödinger, all of which Touma turns down. In the end, they decide to name the cat later, and even then, Touma worries that Misaka 10032 would name the cat as Later. Touma later takes her and the cat, to a used bookstore in order to get a book that would help Index and Himegami Aisa in raising Sphynx better. Before Touma go into the bookstore he throws the cat towards Misaka 10032, despite her remonstrations, telling her that true friendship is born if she is able to break the barrier of her having an electromagnetic field that scares animals.

Then, Misaka 10032 is approached by Accelerator and is forced to leave the black cat next to the store for the experiment to take place. The cat is later found by Touma, and accompanies him throughout the arc. The cat is present during Touma's finding of Misaka 10031's body, his discovery of the Misaka clones, his discovery of Mikoto's involvement in the Level 6 Shift, and later, his stand-off against Mikoto at a A Certain Iron Railway Bridge, which the cat somehow survives, despite the incredible energy Mikoto unleashed during her confrontation with Touma, After Touma comes to, and reveals his plan to defeat Accelerator himself, the cat is left with Mikoto at the bridge, and is later taken by Mikoto to School District 17, where Accelerator begins his experiment against Misaka 10032.

Later, the cat is present during Misaka 10032's visit to Touma's hospital room after the fight, and in the Toaru Kagaku no Railgun manga, is also present with Mikoto and Misaka 10032 bonding moment, though it is asleep during Misaka 10032's talk regarding wanting Mikoto to help her find meaning in living. In the Toaru Majutsu no Index anime adaptation, the cat is last seen with Misaka 10032, finally being able to become close with it.

Silent Party Arc
Misaka 10032 uses the cat to have Mikoto know that she wants to see her. The cat is later with Misaka 10032 as she divulges information regarding the similarities between her and Febrie.

Daihasei Festival Arc
September 19. The cat appears with Misaka 10032, as she becomes curious of participating in the Daihaseisai, though is unable to as she doesn't go to any school. She is later mistaken by Wannai Kinuho for Misaka Mikoto, as the Balloon Hunter event is about to begin and she is nowhere to be found. Awatsuki Maaya takes care of the cat while Misaka 10032 does battle in the competition. She is seen later with Misaka 10032 after she was ousted in the competition. The cat is present when Mikoto talks to her after the end of the competition, as well as her eventual abduction by Shokuhou Misaki, as she collapses from a queer malady that has befallen her.

September 20. After Misaka Mikoto asks Kongou Mitsuko to help her find her Misaka 10032 (which Kongou presumes to be Mikoto's twin sister), she discovers that the cat has been cornered by dogs, still in the same location where Mikoto parted with Misaka 10032. After some little trouble with the dogs, Mitsuko takes the cat, not knowing it is owned by Misaka 10032, until Kinuho points out that it belongs to "Mikoto" from the Balloon Hunter competition. Kongou realizes this and explains to Kinuho that the cat is supposed be owned by Mikoto's twin sister, and that Mikoto asked to help her find her, while she is preoccupied by Misaki's clique. Kinuho does not understand, but otherwise is willing to help, saying that she knows a girl in the swim team that uses animals for her ability, Psychometry. Kinuho leaves to get her cellphone, and while Mitsuko becomes excited at finding Misaka 10032, little did she know that Baba Yoshio is approaching her. The cat is brought along by Mitsuko as she is taken by Yoshio into his trap. Mitsuko is forced to set the cat aside, as Yoshio uses force on Mitsuko in order to get information from her. Kongou tells the cat to get away, but nonetheless is nearby to witness Mitsuko's battle with Yoshio and his robots. Yoshio, being overwhelmed by Mitsuko's tremendous power, sees the cowering cat on a corner, and attacks it, knowing Mitsuko will try to defend it. He is right, and Mitsuko is brought down by Yoshio's robot mosquito. The cat is there to witness Yoshio's beatdown of Mitsuko, and later, the arrival of Kinuho, Maaya, and Saten Ruiko. Kinuho and Maaya later tells Ruiko to take Mitsuko and the cat as well to safety, as Mitsuko's efforts will all be for naught if they do not keep the safe, as the both of them will not be able hold back their anger.

Ruiko later takes care of the cat while she takes Mitsuko into a hospital. After having the girl with the animal Psychometery look into the cat's mind of what happened yesterday, Wannai Kinuho takes the cat as she and Maaya stay with Mitsuko. It somehow later finds its way back to Misaka 10032 after the Daihaseisai.

Ichihanaran Festival Arc
After Misaka 10032 takes off her shoes to rest on a bench after spending time during the Ichihanaransai, the cat crawls into of it refusing to go out. The kitten spends most of its time inside Misaka 10032's shoe for the entirety of her meeting with Misaka Worst.

Trivia

 * It is not known if Misaka 10032 has decided on a name for the cat. Although all the tentative names given by Misaka 10032 could be considered to be male, there is no evidence that the cat is male due to Misaka 10032's somewhat unique sense of humor.