As a nod to its parent series, Extend gave several Unlimited Characters Distortion Drives modeled after/copied from Overdrives belonging to the GG cast. Relius? He gets Nero Angelo, a Vol Tedo-based projectile that functions in the same manner as its English equivalent, Venom's Dark Angel. As of Guilty Gear XX Accent Core (which predates BlazBlue by nearly two years), Venom is voiced by Suwabe, assuming the role from Mikio Yaeda.
Upping the ante, Unlimited Relius receives Ruber Grando (Red Hail in Latin) in CP, thus borrowing another one of Venom's Overdrives... Red Hail.
Further upping the ante is a Gag Reel featuring him in BlazBlue: Chrono Phantasmawhere Relius ends up in a world where he's a good family man. Now who else isa family man?? Notable that the game is just out in Japan, so they may have noticed the English casting.
Creator's Favorite: Noel Vermillion. She's the mascot character of the series, and admitted favorite of Arc System Works producer Toshimichi Mori. She even became the central character in BlazBlue: Continuum Shift. The only thing saving her from Creator's Pet status is that the fans don't (mostly) hate her.
Doing It for the Art: The only explanation for Idle Animations in a fighting game. They will never be seen in normal/serious gameplay.
Spike Spencer was originally told that Arakune's strange voice problem would be created in post-production, but insisted that he replicate the effect of his voice cutting in and out directly in the sound booth. That's what you hear in the game. (He claims to regret this because he was being paid by the word.)
Executive Meddling: Arc System Works does not like it when people post story-related videos, be they merely Arcade mode playthroughs or even joke endings, and they also don't like it when people post direct music rips from Chronophantasma or the previews they've made as DLC for their NAX Music Player. Hope you're actually willing to purchase the game, because the amount of high-quality videos for this series are few and far-between.
Stranger still; the mindset doesn't exist for Guilty Gear. It is likely that BlazBlue having a more plot-heavy and spoiler-filled story than its predecessor (outside of supplemental materials) has something to do with ASW's stance on the matter. This is justified, by Japanese standards, since spoilers are disliked in Japan and this is somewhat normal in Japanese corporative culture.
Fake Nationality: Despite the names, very few are from where you expect. Based on the cities they are born where applicable, along with official material:
Ragna and Jin are English
Noel is Swiss but created in Russia, as was Lambda
Tao is Thai, as in Nu
Bang and Kokonoe are both from eastern Europe.
Kagura and Tsubaki are Canadian.
Makoto is Indian.
Celica and Trinity are Russian
The Clovers are American
Subverted; Litchi is Chinese, as is Jubei. Both are small continuity errors; Jubei created the Hierachical cities, yet was also born in one (the 12th, to be exact), yet Litchi was officially born in Shanghai, which shouldn't exist anymore.
Nu-Gundam: v -13-'s 4th color in her DLC pack is a Gundam.
Gay Man: Bang wearing his pink costume. His butt whistles when he flies!
Clap Loop/The Clapper: Again, Carl. This involves positioning Nirvana right behind the opponent and repeatedly keeping the opponent juggled in the air while throwing them. Only certain characters can escape this loop, and only under certain circumstances.
Assdrill Finish/Asstroll Finish: Relius' Astral Heat, where it's heavily implied he rapes the opponent. Since the first footage of it was done on Ragna, the first one seems to be the more popular.
Entering the realm of meta, Asstroll is also a nickname of a deliberate act to invoke an Astral Finish on your opponent to rub the salt on the loser (though mostly for sports rather than utter insulting), such as delaying a fight and not using your Barrier Burst so your meter becomes 100, and sparing your enemy so the set up attack to ensure Astral would end up not killing the opponent by accident. However, if done poorly and the opponent is smart, this would end up as a double-edged sword as it can cost a match that could've been won.
Joany Actuallyaguy: Mai Natsume from the manga spinoff Remix Heart, a derisive nickname to compound on how hated he/she/they is/are and how confusing his/her/their gender is.
Mikadoperator: The Imperator (Saya). In Japan, she's referred as "Mikado." Therefore, it's a portmanteau nickname.
One of Us: The localizing team did a pretty good job of translating all the medals/achievements in BBCSII and still managed to add in a few puns. Twelve of these medals involve Legion Mode, a mode where the player has to go through anywhere between one to dozens of bases on a map, where the number of bases depends on the difficulty of the map, and fight the characters occupying these bases. Guess what's the name of the medal awarded for clearing the highest difficulty? It's called What You Say. Yup, One of Us.
A rather funny example of this happens in-universe in Arakune's CS Gag reel. It involves him getting caught in what he believes to be a roleplaying game. Hilarity, (and mentionings of several internet memes) ensues.
The Other Darrin: Mostly Averted in the Japanese dub, English is another story however..
Hazama/Terumi is a pretty funny case actually. A lot of fans thought Doug Erholtz originally did his voice, but it turns out it was Erik Davies. The funny part is that Doug would eventually be his voice when Extend was localized and would go on to continue doing so in Chrono Phantasma.
Spike Spencer also did a few lines for him as part of an extra scene in CS 2's Arcade Mode.
Cristina Valenzuela was unavailable to do the added Arcade story for Mu, so Tsubaki and Kokonoe's VA is used instead.
Tony Oliver was replaced by Steve Kramer as Bang's voice in CS 2, this change would stick and he would go on to voice the character in Extend's added scenarios as well as Chrono Phantasma.
Laura Bailey did a few lines for Rachel in CS 2, but unlike the above example, Mela Lee eventually returned to continue voicing Rachel in all subsequent releases.
Sub: Platinum and Taokaka are, as mentioned above, Madoka and Homura. Dub: Noel and Litchi are Homura and Kyoko (ironically, it's their appearances her that probably helped get both of them the roles in PMMM).
Noel and Litchi are Alicia Rue and Lady Sakuya, again a case of the former playing a petite cutie envious of the latter's more generous assets (though they're more closely acquainted than Noel and Litchi are). Their advances on Kirito in Episode 20 become a bit more hilarious when you remember a particular Gag Reel in CS involving Ragna and the Spectacles of Eros. (And speaking of Ragna, he's Agil/Kobatz in SAO.)
Short Run In Peru: Contrary to popular belief, it was always Arc System Works' intention to release Valkenhayn a week late in North America on the PS3. The 360 version release was intended to be simultaneous, however, until the bug was found.
Japanese-wise, this is the title that enables Asami Imai (Tsubaki) and Chiaki Takahashi (Litchi) into well-known actresses outside Japan (since their previous Star-Making Role in The Idolmaster is Japan-only). Though subverted with Kanako Kondo (Noel & the Murakumos), despite practically being in the main spotlight and Noel is incredibly popular, Kanako Kondo has yet to appear in many other anime/VG series. Also this goes for Bang's seiyuu Tsuyoshi Koyama as well.
English-wise, in a bizarre inversion of the Japanese version, this is the definitive Star-Making Role of Cristina Valenzuela (Noel and the Murakumos) as afterwards, she rose from "internet voice acting celebrity in some minor dubs" into one of the most popular voice actresses at this age. A lesser version also exists for Lauren Landa (Litchi), as while she hasn't made as big a jump as Vee, her role here is considered the one role where people start recognizing her. This also promotes Patrick Seitz (Ragna) from just "that voice actor" into this "OMGAWESOMEVOICEACTOR."
To wit, fans have been asking for Kokonoe so much (and so far, to no avail prior to CP's console port), that Valkenhayn's "Help Me, Professor Kokonoe!" segment in Extend exists only to poke fun at the entire ordeal. Mori probably has graduated to Trolling Creator after that announcement around the time of the localized version. The reveal that Kokonoe would indeed become playable rescinded things a bit, but only for the PS3 fans, as 360 fans will not only miss out on Kokonoe, but Chronophantasma entirely. Following that, Kokonoe turned out to be broken as hell and Mori refuses to rebalance her for CP, so—depending on how much you care about tiers vs. character playability—the PS3 fans still may have ended up being trolled despite their "wish" coming true.
To a lesser extent, this has been done with The Imperator/Saya as well, with Mori saying something along the lines of: "We couldn't put Saya in the arcade version but for the home console? Yes, she will be there." Cue Chronophantasma's console release, where it turns out that he was only half right. She assists the final boss, Take-Mikazuchi in battle, but isn't playable herself.
What Could Have Been: Apparently, BlazBlue was meant to be an RPG, but was changed into a fighting game.