Benimaru's English VA in XII and XIII is Eric Kelso, who also voices Paul Phoenix and Jacky Bryant, both of whom, like Benimaru, are blond fighters with Anime Hair pointing upwards.
Kusanagi from 2002 has special battle intros with any weapon wielder (e.g. Whip, Billy, Chang and Choi), calling them out to fight with their fists instead of weapons; basically the same scene in AKIRA with Kaneda (who, like Kusanagi, was voiced by Mitsuo Iwata) calling out on Tetsuo to take on him with his own fists instead of using his powers.
Kusanagi: "Temee! Sude de shoubu shiagare!" ("You [bastard]! Fight me with your bare hands!")
Doubled during his intro against K9999 (who was even voiced by Nozomu Sasaki, hammering home how much he was a Tetsuo-lite):
Yamazaki became a member of the Hakkesshu because he conveniently shared several snake-like aspects with Orochi.
SNK says that most of Oswald's background (which has not yet been revealed) has already been surmised by the fans.
Athena's one-sided romantic interest in Kyo was purely fanon, until KOF:KYO and the '98 and 2000 dramas strongly hinted that she did harbor some feelings for him. (And then they dropped the ball.)
Billing Displacement: XIV has Shun'ei as a new protagonist of the series. However, Kyo and Iori are featured very heavily in the promotion of the game. Kyo is also on the front cover of the PS4 box art along with Iori, Mai and Nakoruru, while Shun'ei was put on the background.
Creator's Favorite: SNK flat-out admits they love Rugal. They designed him from the ground up to be the most badass boss character there ever was (and that's not paraphrasing by much), and that they make him the final boss in Dream Match games because he's their favorite. This would be annoying, if Rugal didn't viciously beat his way into players' hearts the world over, cementing himself as an icon to the fanbase as much as he is to the folks at SNK. The SNK fandom likely idolizes him more than Capcom fans have idolized the likes of Akuma or M. Bison.
Development Gag: May not even have been intentional. Prior to creating Kyo Kusanagi, SNK had drafted his character as "Syo Kirishima", a more archetypal fighting game protagonist. While this was eventually dropped in favor of Kyo, Syo showed up a couple of times in the NESTS arc as a special Striker character. During those appearances, he was voiced by the aforementioned Mitsuo Iwata. Come KOF 2002, Iwata would be voicing Kusanagi, who is a throwback Kyo clone complete with his '95 moveset.
Doing It for the Art: SNK Playmore's decision to stick to the traditional means of sprite creation (dot art, or "pixel-by-pixel") for The King of Fighters XII and XIII over doing cel-based 2D animation (like BlazBlue does) or fully 3D graphics (as Street Fighter IV did). Since XII and XIII are HD games, they needed sprites that would be reasonably sized at 720p, which required a lot of work (they estimated about a year's worth of work for every character's animation set). However come XIV they adopted the 2½D approach Street Fighter IV uses. Still, commendable effort to stick to such a traditional means of sprite creation at a time where it was becoming increasingly infeasible (both due to the advancement in display resolution requiring larger and more detail-heavy sprites and the diminishing number of talented artists who could still do that kind of work).
Executive Meddling: When Eolith sponsored Playmore so they could pick up the scraps from SNK's fallout, they requested a "Korean Athena". The end result was May Lee.
Exiled from Continuity: K9999, mainly due to him being too blatant an Expy of Tetsuo Shima. So much so, he was the only character present in the NESTS arc not to appear in 2002 Unlimited Match; SNK-Playmore created Nameless with the specific purpose of replacing K9999 and retconning him away.
In order to differentiate Kyo from his clones, fans often refer to his NESTS depiction as "Shin Kyo" (as in "True Kyo").
Yaoiori for Iori, thanks to all of his Foe Yay with Kyo. The infamous "Yagami is I'm-a-gay backwards" joke didn't help in this regard; his tendency of throwing out ambiguously gay lines in his special intros with Kyo probably helped even less. This is teased to no end by various official/fan works.
Fathena for Athena's appearance in XII and XIII: Moeness and chubby legs.
Yuri's parody of the Shun Goku Satsu, the Yuri Chou Enbu, is sometimes called the Shin Yuri Satsu.
Kim is sometimes nicknamed as The Beijing King, thanks to the My Way Entertainment fan dub of one of the Fatal Fury OVAs.
Shingo's notebook full of information on his techniques has been known as both the Death Note and GameFAQs thanks to his HSDM in 2002: Unlimited Match.
Mongolia - Maxima, with one of his normal moves being a Mongolian Chop. It's from Japanese Mugen community where they call him such due to parody videos involving him doing that move a lot.
Ass Crimson - Ash Crimson from The King of Fighters 2003, who is so flamboyant that he might qualify as a Gorgeous George. He's also sometimes called as Ass Crapson, Fish Crimson (stemming from an unfortunately squished uppercase "A" in one of the XI menus resembling the letter F) and Fist Crimson. AshleyCrishit and Ash Shitson are less popular but still common variations of the above. You can tell that a lot of people hate Ash, but SNK (and the Japanese) just love him. Of course, all fan nicknames for Ash Crimson became discredited once his true motives were revealed.
Chuuni for Shun'ei in XIV due both to his design giving off vibes of the stereotypical chuunibyou teenager and the similarity of his name to the term.
To answer the first question: Is Geese Howard dead or alive? There ya go.
Luise's profile and storyline in the Maximum Impact series were written to be deliberately different from one another, most likely to prevent spoilers.
Lying Creator: The devs for XIV says that King of Dinosaurs was based on a sketch that one of them drew about a dinosaur-themed wrestler and they grow attached to it, and they deny that he is Tizoc. Yet in the game it's made quite obvious that he IS Tizoc. Though it's most likely to avoid spoiling his identity, but as early as the game previews many fans had guessed it.
Marth Debuted in "Smash Bros.": Maxima was originally in an old SNK beat 'em up called Robo Army. The other main character, Rocky, serves as his alternate Striker in 2000.
Also in XIV, the characters from SNK's pachislot games like Muimui, Love Heart and Alice.
Name's the Same: Despite being named Heavy D!, the leader of the US Sports Team is not the rapper...
Katsuhisa Namase voiced Joe in KOF '94. Nobuyuki Hiyama has taken over the role since then, until XIV where Kozo Mito took over.
Robert Garcia: Kazuhiro "Kay" Inage was replaced by Mantaro Koichi, who voiced Robert from KOF '96 to 2003. When Robert popped up as a Secret Character in XI (which was based off of his appearance in Mascot FighterNeo Geo Battle Coliseum), Inage returned to voice Robert, and continues to do so in XII and XIII. Come XIV, Inage gets replaced by Go Shinomiya.
Bunsyu Shinoya takes over for Ralf in XII. In English, Scott Casey in the Maximum Impact series, Jeff Manning in XII.
In English, Clark went from Sean Michaels (Maximum Impact) to Eric Kelso (XII).
Kim is voiced by Kazuhiko Nagata in XII, succeeding Satoshi Hashimoto (Hashimoto voices terry until XIII, where Takashi Kondo takes over for XIV).
Akoya Sogi (who has voiced Mai from the beginning up to XI) has been replaced by Ami Koshimizu as of KOF Sky Stage. Given that Sogi has apparently retired, it's a safe bet to assume that Koshimizu will take over in all subsequent appearances. This could also be the reason behind Mai's absence in XII.
For Kyo, Andrew Roth (his English VA in the Maximum Impact series) was replaced by Peter von Gomm come XII.
His Japanese Voice is also changed for XIV, with Tomoaki Maeno taking over Masahiro Nonaka.
Between '94 and '98, Athena's voice changed as much as her clothes, with one for every game. In order: Reiko Fukai, Moe Nagasaki, the aforementioned Tamao Sato, Chris Yukina, and lastly Haruna Ikezawa, which was the one who stuck. It can be presumed that this was because SNK was testing out seiyuu for her.
Krizalid is a rather perplexing example in that both of his seiyuu are used in 2002 UM (Yoshiyuki Iwamoto for him as a standalone character, Eiji Yano for him as one of Original Zero's Strikers). Semi-justified since they are two different Krizalids, the one who backing Zero being a clone of the one who hosted the '99 tournament.
En masse for XIV, many voice talents got replaced, not the first time it happened in the series as one can see above but XIV took many mainstays out in one go; characters that had the same voice for decades (Kyo, Kensou, Yuri to name a few) were finally, but sadly, gone. And also shockingly, despite still being active in 2016, Nobuyuki Hiyama did not return for Joe. The only characters who didn't get recast were Geese, Benimaru, King, Mai, Athena, Chang, Choi, Kula, Maxima and Tizoc as the King of Dinosaurs.
Nakoruru subverts this in XIV, though. Harumi Ikoma, her very original voice actress, did not return for her. However, Mai Nakahara, who was voicing her during her appearances in Samurai Shodown's Pachislot titles reprised her role.
Haruna Ikezawa voices Foxy in 2001 and 2002 Unlimited Match, in addition to Athena.
Richard Meyer is voiced by Kong Kuwata, who also voices Geese Howard and Duck King.
Eric Kelso voices Takuma, Clark and Benimaru in the English version of XII and XIII.
Monster Maezuka voices Ralf, Benimaru, and Choi.
Masahiro Nonaka voices Kyo's clones, Kyo-1 and Kyo-2. Subverted with evil, magical doppelganger Kusanagi, who is instead voiced by Mitsuo Iwata.
However, KOF Sky Stage seems to be using Nonaka instead of Iwata for the voice of Kusanagi, which of course plays this trope straight again.
In XII and XIII, he shares an Englsh VA (Peter von Gomm) with Ash of all people.
King shares her seiyuu (Harumi Ikoma, who also is the announcer in KOF '96, KOF '98, KOF XI, and KOF XII) with Blue Mary. Ikoma also voiced King's brotherJean/Jan in KOF: Kyo.
Greg Irwin voices Joe and Robert in the dub of XII/XIII.
Kazuhiro "Kay" Inage (who voiced Robert in KOF '94 and '95, and returned in XI) also voices Lucky. Mantaro Koichi (who voiced Robert from KOF '96 to 2003) was also the announcer in '97.
Kay Inage also voiced Mizoguchi in Regulation A. Both he and Robert are semi-shotos with a flying kick move, both have the Tiger as their Animal Motif, and EX Robert's HSDM in 2002: Unlimited Match ends with him firing a Tiger-shaped Haoh Shokoken, identical to Mizoguchi's "Tiger Bazooka Attack".
In XIII, Sonosuke Nagashiro voices both Hwa Jai and Ash (and Saiki, by extension).
Throw It In: Hyena's lines were devised in a collaborative effort between the seiyuu of Hyena, Alba, and Soiree (who consequently became good friends through the experience).
Krauser's Gigatech Cyclone was actually taken from the spinning supers (i.e. the Senpuuken/Hadou Senpuukyaku) utilized by he and Terry in the Fatal Fury 2OVA. His youthful beauty and lack of a mustache and scars, were not retained, despite being well recieved by some fans.
What Could Have Been: Beside the various prototype designs of characters (many of which can be seen as Strikers in 2000), many plot points were shafted or altered:
Orochi Iori was originally planned to be the final boss of '97 (remnants of this manifest as Iori being a Bonus Boss in said game if you beat Orochi with Kyo).
Kyo and Iori were going to be dropped from '99 to put emphasis on K'. They became secret characters instead.
The biggest "what if?" would have to come from 2001. One could only imagine what direction the series would have taken if SNK hadn't gone bankrupt after 2000.
Believe it or not, it was planned for Terry to actually die at the climax of '99note One of the Fatal Fury team endings give off this vibe by having Terry stay behind in the collapsing base, but The Stinger reveals that he survives. Luckily, head management disagreed and brought him back in 2000, avoiding what would have been a shocking Player Punch and the ensuing barrage of Internet Backdraft. However, the "what if" aspect of his death was played up for the remainder of the saga to the point that Blue Mary told Terry how his teammates (or more specifically, her) were worried about him in the team's 2000 ending.
Kim was supposed to debut in the first Maximum Impact under the alias of "Mr. Taekwondo", akin to "Mr. Karate". Instead, Chae Lim took his place, and Kim popped up in the sequel as his good 'ol regular self. Chae Lim herself was chosen over the likes of Jhun Hoon, May Lee, and Buriki One character Seo Yong Song.
Originally, Chang and Choi were going to be paired up with another dangerous criminal to from the "Fugitive Team". Kim was a last-minute addition, thus setting up the whole "rehabilitation" plot. This concept would be revisited for XIV, with Chang and Choi teaming with Xanadu to form the Villains team.
King's Surprise Rose super move from Art of Fighting 2 was her original DM in '94 but was scrapped for some reason. King's designer then came up with the Illusion Dance DM and it was well received. It was turned back into a DM in 2002: Unlimited Match and XII.
Ralf (and presumably Clark) was supposed to have a moveset revolving around grenades back in his KOF debut as a Shout-Out to Ikari Warriors. This was scrapped due to a possible case of game breaking mechanics.
Lampshaded in the intro dialogue between Kyo and Clark in XIII, wherein Clark explains that the grenades he's wearing are duds, so there's no danger of them going off if Kyo uses his fire on them.
Heidern's moveset and their names were so strange that the designers were going to make him an alien as explanation for his "abilities." However, the lead designer became attached to the character, giving him a tragic backstory instead and keeping him as a human.
Saisyu was supposed to have died during his Early-Bird Cameo in '94. His appearance in the following game was a last-minute addition.
"Chris of the Flames of Destiny" was originally going to have black flames, but the idea was dumped as they would have been too hard to notice in his rather dark stage.
According to the Developers' Blog for XIII, Chang, Malin, Momoko, and Oswald were meant to be in the game. Chang was reduced to a cameo in the India stage, whereas the other three cameo in endings (the Women Fighters Team, Psycho Soldiers Team, and Ash Crimson, respectively).
And Chang (along with Choi) makes the customary Kim Team ending cameo.
Vanessa was supposed to be playable in '99, but didn't make it in time. She makes an Early-Bird Cameo as a Striker in the '99 Evo console release.
The Neo MAX supers in XIII were at first created as extensions to normal supers, but because of testing feedback they were eventually changed into stand alone supers. A few Neo MAX supers in the final build still look like they were supposed to follow up on normal supers, some of them only effective gameplay-wise when used as such.
Adelheid was apparently meant to be playable in XIII, based on some full-body and winpose sketches by Eisuke Ogura.
If unused◊ concept◊ art◊ for '98 and '99 is any indication, it might have been intended for Adel, Rose, and Magaki to join the series as early as the NESTS Chronicles. In particular, one of Rose's prototype designs is shared with that of Whip.
Foxy, who made her debut in 2001, originally wasn't meant to be playable. When it was decided that she'd be added to the roster, it was intended for Diana to join her, although this didn't pan out because of time constraints and Diana remains to this day an NPC.
Raiden's first playable entry in the KOF series (prior to XIII) was going to be in 2003, but the developers eventually decided on using Tizoc instead.
His 'Big Bear' persona was also going to appear in 94, but scrapped in favor of Yuri being added.
Billy Kane was planned to be playable in 94 but scrapped due to limitations.
Whip was planned to enter the series as early as 96, but was pushed backed till 99 due to Leona being introduced.
The introduction for '98, "Cipher", as well as the ending theme, "Zero", had a sound clip in it with rather vulgar language in it: "Pay dat shit like he just got yo motherfuckin' check and he's gonna pick it up at the bank." In the foreign releases of the game and the 15th Anniversary CD, this clip has been edited out and replaced with static, which is not present in the OST.