Riko Mine

"Let's meet again, my rivals. I'm not gonna forgive you if anyone besides me takes your lives."

Riko Mine (峰 理子 Mine Riko) is a female student of Butei High school. She is a friend of Kinji's, whom she calls Ki-kun, and is enrolled with him in the Butei Inquesta department. She is ranked A (Second highest rank). Although known as the biggest idiot in Kinji's class, she seems to hold a lot of information including info on the students of Butei High school. She likes customizing her uniform into Lolita style and playing dating sim video games (However, she looks too young to buy them so she asks Kinji to buy them for her.)

Appearance
Riko and Aria have similar traits: small stature, the title of "Quadra", twin-tail hairsyle (in Riko's case, her hair is not entirely split in half unlike Aria), and being the fourth generation of their families.

Personality
She usually puts on a facade of stupidity, but some times, usually during tough situations, she breaks the facade. Kinji calls this side of her personality "Dark Riko". With the facade removed she uses rough language, her eyes emit an intimidating glare and she refers to Aria as Holmes (French: Olmes) instead of Aria. She is also one of the few people who knows Kinji's secret.

History
Her most valued possession is a cross made of Irokane. This cross allows Riko to control her hair at will. Vlad eventually steals this cross, prompting a series of events in which Kinji and Aria retrieve it by infiltrating Vlad's place. It soon turn out that after her parents die in a car crush at the age of 8 Vlad take her in by pretending to be her relative but he lock her up in an underground dungeon to conduct an experiment of impregnant her a 5th Lupin descendant. She was imprison there completely naked with a ragged piece of blanket with her leg chain up,there she was force to eat rotten rat meat & drink muddy water to survive.

Plot
Near the end of the first volume, Riko reveals that she is a descendant of Arsene Lupin. Although she is the descendant of Arsene Lupin, she was born with no special abilities. Her real name is Riko Mine Lupin IV. Riko also reveals that she is the Butei Killer. She appeared to have an inferiority complex concerning the first Lupin and wanted to escape his shadow. Her plan was to make Aria and Kinji become partners so it could mirror the situation of Sherlock Holmes and Watson. Defeating both of them would mean she would become better than her ancestor Arsene Lupin who couldn't defeat Sherlock 100 years ago. She despises being called "4th" because she feels it removes her personal identity, as such she prefers "Riko".

Equipment
Her weapons of choice are double Walther P99s for daggers for melee. Like Aria, she has earned the title of "Quadra".

Kinji Tohyama
Riko loves to flirting with Kinji a lot through sexual manner. However, she develop feelings for him after defeating Vlad.

Trivia

 * Riko's last name, "Mine", is a tribute to Fujiko Mine from Monkey Punch's Lupin III.
 * Riko in episode 4 reveals that Kinichi is her boyfriend/lover.