Zodiac P.I.

To solve the crime, she needs your sign!

A manga series by Natsumi Ando, originally published in Japan as Jūnikyū de Tsukamaete starting in late 2001. The series is published in Japan by Kodansha, and it was published in English by Tokyo Pop; the English Tokyopop version is out of print as of August 31, 2009.

The story followed 13-year-old Lili Hoshizawa, who uses horoscopes and astrology to solve crimes, accompanied and assisted by her male childhood friend Hiromi after he returns from 10 years spent in America for college. Lili uses the Star Ring to tell fortunes and, at times, to transform into the disguise of Detective Spica, in which no one recognizes her, except Hiro. The ring was left to Lili by her mother, who disappeared some years ago. Using the ring, Lili summons an appropriate Zodiac Sprite based on the birthdate of the person most heavily concerned in the crime. Then she'll ask for the horoscope of the victim on a specific date that is connected to the crime. Along with the horoscope, the spirit will give her a clue so she can solve the crime.

Tropes used in Zodiac P.I. include:

Allergic to Love: Poor Hiromi breaks out in spots if a girl touches him until the third volume, where it mysteriously goes away (at least for Lili).
- It's because Lili was the source of the "allergy", after she didn't know to meet him before he left, when they were children.
Badass Normal: Hiromi
Bishonen: Zeus, Hiromi, Lili's dad, Prince Ryo, Satoshi, and Mr. Izumi
Brainwashed and Crazy: Sirius spends the entire last volume brainwashed by the Big Bad.
- Actually, she spends pretty much the entire series brainwashed. Hence why she can't remember she's Lili's mother.
Childhood Friend Romance
Child Prodigy: Hiromi, who left for America to attend college. However, he goes right back to attending high school after coming back to Japan...
Emotionless Boy: Aquarius.
Forgotten Childhood Friend: When Hiromi first shows up, Lili doesn't remember him...It takes a little while for her to actually realize he's her old friend from kindergarten.
Genki Girl: Lili, and quite a few of the Zodiac Sprites.
Great Detective: Lili and her father. Also, Hiromi at the end.
Handsome Lech: When Leo's spirit appears, he chides Lili's polka-dot panties. She doesn't appreciate it.
Hostage for Macguffin: An invoked case -- Sirius and Zeus' fiancée faked this to see which one Zeus truly valued. When Zeus briefly hesitated to make the exchange, his fiancée was so distraught that she flung herself off the cliff.
Hot for Student: A darker, creepier example in one of Lili's cases. He's been kidnapping girls and hiding them in his classroom, intent on "making them love him".
Hot Mom: Lili's mother was/is quite a looker.
Hot Shoujo Dad: Lili's father, Inspector Hoshizawa.
Improbable Age / Older Than They Look: Sirius, Lili's rival, looks to be a little older than Lili...she's actually somewhere in her 30s. And she's Lili's mother.
Inspector Lestrade: Inspector Hoshizawa.
Love Makes You Evil: Crossing over with Love Makes You Crazy. The Big Bad, Zeus, went evil because Spica pushed his fiancée off a cliff, which resulted in her falling into a coma. Or, so he thought...
Love Redeems: Zeus
Luke, I Am Your Father: Sirius is Lili's mother.
Magical Girl
Missing Mom: Lili hopes to eventually find her mother by becoming a famous detective.
Mood Whiplash: Some of the cases are decidedly darker than the rest. Compare one case, where Lili has to locate a stolen bust, and another, where Lili's classmate is found murdered behind the gym. Also occurs in one of the final chapters; the overall mood is pretty dark, Lili must hurry to solve the case, and defeat Zeus...and then she summons the final Zodiac Sprite, who is all smiles, cheer and warmth, and affectionately calls Lili "Kiddo" almost immediately upon appearing. Lili even Lampshades this.

Lili: "Wow, you sure do lighten the mood..."

Pocket Protector: Zeus shoots Lili in the chest in the final chapter...but she turns out to be completely unharmed, as the bullet struck the diamond pendant (that originally belonged to Zeus's fiancée) she was wearing under her shirt.
Rich Bitch: Hiromi's sister Megumi.
Single-Minded Twins: the Gemini spirit/s.
The Power of Love: It breaks Sirius' hypnosis, and wakes Zeus' fiancée from her coma.
Tsundere: Io (spirit of Taurus) seems very dere at first, but as Chiron (Sagittarius) found out, she doesn't take kindly to being put down.
Western Zodiac: You'd never expect it. For the record, Lili is a poster child for Aries, and Hiromi is Capricorn.
Wholesome Crossdresser: Lili forces Hiromi to dress up as a girl so they can investigate an all-girls school.
Yamato Nadeshiko: The spirits of both Virgo and Cancer.