Kaori is quite a beautiful woman, yet since they became partners she fails to get Ryo horny (unless he doesn't know it's her). At first it seemed strange... Then, reading the manga version of the Union Teope arc I found the answer: Ryo told Kaori that if she was to be his partner he wouldn't consider a woman anymore, and Kaori accepted. After the erection in that scene, Ryo almost stopped having erections from Kaori when he knew it was her.
Inspector Hirotaka Takeo looks like Hideyuki with darker glasses, to the point that Kaori briefly mistook him for Hideyuki's ghost, yet Ryo declares they look nothing alike. At first it seems Ryo is being an idiot as usual... Then you remember: Ryo tends to forget faces but remembers well the most notable characteristics of a person (best shown in the second story with Kasumi Aso: at first he couldn't recognize her due her civilian clothes, but screamed "Little Flying Ass" as soon as he saw a gymnastic leotard in the window of a ship), that, in Hideyuki's case, is his carefree and all-around nice personality, completely different from the more cynical Takeo.
This leads to another case of Fridge Logic: upon meeting Kaori, Ryo immediately recognized her as the 'Sugar Boy' he had met years earlier (the salient characteristic was her being a Bifauxnen and asking for advice to the strangest people). He just doesn't like talking of the past.
At the start of the series, a yakuza boss felt capable of having Ryo killed. Later in the series, the five most powerful yakuza clans of Kanto feels that, even together, they're no match for City Hunter. At first it seems strange... Then you realize: Ryo is the only person to have ever defeated Union Teope, where even other criminal syndicates were being destroyed by them. When the first yakuza boss made his threat Union Teope had just started pulling back, but after that...
In the second-to-last story arc Ryo deconstructs the Anguished Declaration of Love, noting that when it seems you're about to die the instinctive need for reproduction will take over and may make you believe to be in love, and explicitly says that Mick knows this well. The obvious question is: how much of Ryo and Mick's perversion stems from their lives being in constant danger?
Ryo and Kaori tend to have money problems. With what they earn, it seems strange... Then you notice how often they have to repair parts of their home from the damage they cause in their fights (plus Umibozu booby trapping a large area of the house to stop Ryo from jumping the daughter of his commanding officer during his days as a merc and a sabotaged airplane ramming the building, and the fact that the .357 Magnum rounds that Ryo uses all the time are friggin' expensive...
The revolvers we see Ryo using are all chambered for .357 Magnum (his Python), .38 Special (his back up M37, can also be fired by the Python) and .41 Magnum, with the only things they have in common being them being intended for police use (the Special had actually been created for military use, but became the prototypical police revolver round in the 1920s and is the standard round for Japanese police revolvers). Early on, Ryo states that he does those police jobs that the actual police can't do for some reason.
About rounds and guns... The choice of handguns for all sweepers in the series seems to have a deeper meaning: the General's arm-mounted assault rifle is the symbol of him being a military commander for a drug cartel and of the lengths he'll go for his job; Umibozu mainly use a .44 Magnum, used by either law enforcement officers with little concern for collateral damage (see Dirty Harry for a somewhat realistic example) and big game hunters, and Umibozu, while still a Hitman with a Heart, is less concerned about defending civilians than Ryo is; Snake, Umibozu's traitorous comrade in his mercenary days, used a .38 Special gun, ineffective against Umibozu, and an AutoMag, a range toy for rich persons, as an hint that he rarely thinks things through; Silver Fox subverts Good Guns, Bad Guns by carrying a Browning Hi-Power, something that makes perfect sense due his militaristic theme and habit of disguising as an ally; Miki has been seen with a Colt M1911A1 and a King Cobra, the first an American military pistol symbol of her past as a mercenary and the latter a law enforcement pistol that can be linked to her calming influence over Umibozu; Bloody Mary carries either a PPK/S or a Glock 17, the spy weapon when she was The Mole and the Glock when she returned as an unquestioned ally; the Bat too uses a Colt M1911, and, given his rivalry with Ryo, can be linked to the debate of semiautomatics versus revolvers (they both use some of the most popular guns of their category); Kenny Field used a Colt Government Model, with his job as a bounty hunter being practically killing criminals on the US government's behalf; the Black Lizard's Browning Hi-Power is more a sign of what he wishes to be; the hypnosis-using assassin lack of a gun is a sign of the fact he never needed one; Mick Angel's use of a Desert Eagle in .44 Magnum (an hunting weapon) gets a new meaning when you find out he's the American City Hunter; and Kaibara's Colt Anaconda, practically being a larger Python in .44 Magnum, is a symbol of his relationship with Ryo.