A top student of Assault Side, who, for some reason, demoted himself to the more rear-line Inquest Side. When sexually aroused, he enters a state called "Hysteria Savant Syndrome" (HSS), also known as "Hysteria Mode".
Accidental Pervert: And considering how his power works, this can be a problem… or save his life.
Blessed with Suck/Cursed with Awesome: HSS grants him superhuman abilities, but it is only activated by sexual arousal, and under such a state Kinji turns into a suave ladykiller, which he thinks is detrimental to his academic life.
Humiliation Conga: He was forced to mull leaving Butei after he and his (supposedly-dead) older brother Kinichi was subjected to this after the latter's rescue attempt aboard a sinking ship, but with the shipping company unwilling to take responsibility and instead scapegoating him.
Mistaken for Pedophile: By his classmates as one due to his closeness to the diminutive Aria. She is the most effective catalyst for his HSS. For example, in Episode 10, he managed to resist arousal from Riko in just her lingerie, but couldn't hold on any longer once he saw Aria taking off her socks.
A diminutive top student of Butei High's prestigious Assault Side. Looking for a fitting partner, her attention falls on Kinji, whom she quickly declares her "slave". She is also the great-granddaughter of the most powerful and intelligent detective in history, Sherlock Holmes.
Animal Motifs: Cats. She is fond of "Leopon" stuffed cats, some key scenes involving her have random purrs, and in Episode 2 she even growls like a cat. In Episode 6 Shirayuki even calls her a "thieving cat"note A derogatory term to a female romantic interloper; this is frequently used in Japanese live-action drama shows for freeloading with Kinji.
Clear Their Name: Aria's primary motivation for attending Butei High is to help clear her mother, Kanae, of charges of being the "Butei Killer", which automatically sent her to 862 years in prison. If successful, Aria could shave off centuries of prison time for her, and at the best-case scenario, even clear her altogether.
Scars Are Forever: After a brush with death during the bus bomb incident, she has since kept a small X-shaped scar on her forehead (now hidden by her hair) as a reminder.
Shana Clone: Short, aggressive, long red hair, Grade S Zettai Ryouiki, tsundere, has the same affection for peach buns that the original had for melon bread and voiced by Rie Kugimiya to boot. She's possibly the 5th Tsundere Wonder.
Freudian Excuse: Sick of being constantly referred to as "Lupin the 4th" by Vlad (pretending to be a relative), Riko was forced to join I-U, hoping to kill a Holmes and finally break free of her great-grandfather's shadow.
I Am Not My Father: Ultimately subverted in the end, when, after defeating Vlad, who brainwashed her into doing his bidding by hammering the title onto her, she regains her pride of her heritage as Lupin the 4th.
Malicious Misnaming: She pronounces Aria's name like in French instead of the correct spelling i.e. "'Olmès" instead of "Holmes". Well... that's the idea at least. No-one in France actually pronounces it that way.
Master of Disguise: Riko Mine is another thief character with the ability to disguise themselves excellently. Because she is the great-granddaughter of Arsene Lupin, and Holmes's nemesis.
Born in the Wrong Century: As noted by Kinji, Jeanne shows shades of this. She's refined, wears plate mail, wields a zweihander (two-handed sword), doesn't know what a vending machine is, and dislikes skimpy clothing (including modern school uniforms, even her Butei uniform). This may have stemmed from growing up without seeing the world beyond I-U's auspices.
Aria's mother currently spending an absurdly long 862 years in prison for charges of being the "Butei Killer".
Clear My Name: Aria's motivation for attending Butei High is to clear her of charges of being the "Butei Killer". If successful, she could shave off centuries of prison time for her, or perhaps even clear her altogether.