This A Certain Magical Index side story consists of Volume New Testament SS of the light novels.
Index uses Touma's laptop to solve some online puzzles and wins a sum of money for it. Touma gets the envelope in the mail and gives the money to Index, saying it is hers and she can do whatever she wants with it, and advises her to spend it wisely. She happily leaves their apartment with Sphynx.
She decides to buy Touma a present and wonders what she should get. She runs into Mikoto and Kuroko, who exit a shop disappointed that the new manga releases have not come in yet. Index acts hostile and says they can't take her money. Naturally, Mikoto gets annoyed and says she was planning no such thing. A big-rig zooms by and blows Mikoto and Kuroko's skirts up. Index gets embarrassed and offers a few bills to compensate them, but Mikoto says it doesn't matter and tells her to cut it out.
After leaving them, Hyouka Kazakiri materializes and greets her. Index muses that between Hyouka and Arisa Meigo, she has a lot of friends who aren't exactly human, but they're good friends and she loves them nonetheless. Hyouka asks if she decided what she wants to get Touma. Index excitedly starts listing various foods, but Hyouka scolds her and says she should get him something meaningful that he would actually appreciate, not just something she wants. A nearby cafe waitress accidentally drops a glass bottle, which breaks. Maika Tsuchimikado shows up and calls up some cleaning robots to sweep up the mess.
Hyouka vanishes back to her state of invisibility and intangibility. Index gets weirded out by the cleaning robots, and asks if Maika is a summoner mage. Confused, Maika asks if she has never noticed the robots before. After Index tells her of her plight, Maika suggests she get Touma a new steam oven. Index agrees, since their oven is very old and she's excited that Touma will be able to cook better. The two of them go to an appliance store and order a steam oven. Maika gets annoyed when Index doesn't know what Touma's address is even though she lives there because she never bothered to look around, but Maika knows it and completes the form. Index thanks her and starts walking home with Sphynx.
Index suddenly goes into a back alley and tells whoever is following her to come out. Sphynx scratches her hand and slips away from her. An Egyptian magician with cat-like eyes and a cat-eared hood walks up. Index identifies her as a priestess for Bastet the Goddess of Cats. Thanks to this, she can see and hear through any cat and control them. She was trying to use Sphynx to read her mind and gain her knowledge, but it didn't work, so she decided to catch her the old-fashioned way.
Index reveals that she was on to her ever since this morning. The truck that sped by Mikoto and Kuroko, the bottle that the waitress dropped, etc, all had extremely tiny hieroglyphics on them. Thanks to her perfect memory and incredible analytical skills, she was able to notice them. The hieroglyphics were used to secretly insert information into Index's head. Index also deduces that the magician wants The Book Of The Dead from her memories.
The magician says her deduction is correct, but she made one mistake. She is not a priestess for Bastet the Goddess of Cats, but for Sekhmet the Goddess of Lions. While Bastet symbolizes fertility and protection, Sekhmet symbolizes war and bloodshed. She grows lion-like teeth and her right hand turns into a massive lion-like paw with extremely long claws. She scratches her own chest to make a blood sacrifice to her goddess, then says she can extract knowledge from a person by splitting their skull and then examining their brains. She lunges, but gets shocked when Index just stands there and starts talking to her telepathically.
In a flashback, Index annoys Touma by watching Magical Powered Kanamin and loudly nitpicking everything. Since she has photographic memory, she can notice all the animation errors.
The magician gets so shocked and confused by Index's lack of reaction that she trips and her own momentum makes her crash into the ground hard. Index was counting on that, knowing she cannot possibly fight her directly. Index deduces that the woman actually is a priestess of Bastet, but merely borrows some aspects of Sekhmet. The Book of the Dead is unique for each person, so who does she want to contact?
She reveals that she grew up admiring an actual priestess of Sekhmet and loved her like an older sister. The priestess refused to take her on as an apprentice, so she followed her everywhere and observed her to learn a little of her magic. Eventually, the priestess died, and she was devastated to realize she didn't actually know anything about her. She didn't know her past, her likes, her dislikes, her accomplishments, etc. She is not crazy enough to want to resurrect her idol, she just wants to read her personal Book of the Dead so she can know everything about her and make sure she is not forgotten. She entered her idol's tomb and tried to read her book, but tomb robbers broke in earlier and tore it up. Thus, she inserted the book's fragments into Index's mind so her knowledge could reconstruct it.
Index takes pity on her and reveals that she can access her idol's Book of the Dead. Speaking in her idol's voice, she addresses her as Leep. She tells Leep she loved her like a little sister, and that she refused to take her as an apprentice because she didn't want her to follow her dark path. She is proud that she became a priestess of Bastet, for she can do a lot of good in the world and shower it in miracles, unlike her, who can only shower it in blood. She says Leep was always following her, but Leep has surpassed her long ago.
Glad that she finally knows her idol's true feelings, Leep cries tears of happiness and passes out with a smile on her face.
Index comes home and tells Touma she's hungry. He asks how her day was, but she brushes the question off and says he's going to love it when the new steam oven arrives. While he looks on confused, she pets Sphynx and says it was a wonderful day.
- A Day in the Limelight: For Index.
- Continuity Nod: Index mentions Arisa Meigo from the Miracle of Endymion movie.
- The Greatest Story Never Told: Index's adventure is only known to herself and Leep.
- No Name Given: Leep's idol is never named.
