|Name in Japanese||峰理子|
|Romaji Translation||Mine Riko|
|Debut (Anime)||Episode 01|
|Debut (Light Novel)||Volume 01(2nd Ammo)|
|Appears in||Anime, Light Novels, Manga|
|Voice Actor (Japanese)||Mariya Ise|
|Voice Actor (English)||Luci Christian|
|Skill Rank||Rank A|
|Title|| Butei Killer|
Walther P99 Semi-Automatic Pistol (two)
"I'm not gonna forgive you if you are killed by someone other than me!"
Riko Mine Lupin the 4th (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.) Her weapons of choice are double Walther P99s for handguns and double daggers for melee. Like Aria, she has earned the title of "Quadra". Riko is apart of Team Baskerville (Aria and Kinji are suspicious that she will betray them), who chose the affiliation Deen, yet the most of IU choose Grenada, and she was formerly part of that group. It is unkown on which side she will act on. She often gives others nicknames (Reki = Rekyu, Kinji = Ki-kun, etc. ). She also loves to flirt with Kinji a lot through sexual manner.
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.
It soon turn out that after her parents die in a car crash at the age of 8, Vlad took her in by pretending to be her relative but he locked her up in an underground dungeon to conduct an experiment in creating an ideal 5th Lupin. As it turned out that Riko didn't inherit the Lupin bloodline's superior gene, she was branded a failure. She has been imprisoned there for a long time and was forced to eat rotten meat and drink muddy water to survive. It was said that because of her malnutrition that she has a present small stature. And because she could only wear ragged clothes in the whole time of her imprisonment, she developed a love for fancy clothes.
Her real name is Riko Mine Lupin IV. Riko also reveals that she is the Butei Killer. Although she states that the name is wrong as she never killed any of her victims, but instead she was the one that kidnapped those who had disappeared. 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".
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. She has a height of 147 cm (4'10") and weighs 54 kg. The only difference between them is their hair color and breast size.
Her most valued possession is a cross made of Irokane. This cross allows Riko to control her hair at will. She hides it under her tongue when she was imprisoned naked in an underground dungeon. Vlad eventually steals this cross, prompting a series of events in which Kinji and Aria retrieve it by infiltrating Vlad's place.
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 . Riko loves to sexually tease Kinji.
It is obvious she harbors a grudge towards Vlad due to her history. As such, usually the mention of him or his mere presence can turn her into a vengeance-seeking monster.
It is implied that she has actually fallen in love with Kinji, though the time period for when it may have acutally happened is somewhat ambiguous. Since she has shown great affection towards Kinji, she has the extremely bad (good?) habit of sexually tempting him constantly, which has, of course, gotten her into trouble with Aria and Shirayuki in the past.
She holds some hostility towards Aria because Riko had originally planned to kill her to win back her freedom. But after specific events, Riko has lost that kind of hostility. However, Riko sees her also as a rival for Kinji as well.
- Riko's last name, "Mine", is a tribute to Fujiko Mine from Monkey Punch's Lupin III.
- Riko in episode 4 alleged that Kinichi is her boyfriend/lover.
- Riko makes many attempts on having sex with Kinji
- Riko easily gets "turned on". Ex (From the LN): "Abnormally excited, Riko stuck her hands into her blouse, making what appeared to be punching movements from inside."
- All her clothes can be used as a parachute.
- Riko's height is directly caused by the lack of nutrients from her childhood imprisonment.