Actor Allusion: One of the roles of Sumire Uesaka in this game is the Fubuki-class destroyer. Not exactly important at first glance, but remember that "Fubuki" is Japanese for "Blizzard". Which brings to mind the Red Baron moniker from another character she played: Nonna from Girls und Panzer.
Ascended Fanon: The anime adaptation takes some in-jokes from both the fandom at large and some of the spinoffs and canonizes them.
Akagi's Big Eater status comes front and center, after Fubuki witnesses the huge platter of katsu (or bauxite) curry she ordered. Kaga gets foisted with this as well come episode 6 (while her serving appears twice as large as Akagi's, it's likely that Akagi was halfway through her plate).
Inazuma's "nanodesu", despite not being used often in the game proper, turns into a proper Verbal Tic, used in all but one of her lines in Episode 2 and it gets over-killed in Episode 6 with about 17 instances of it — the most of out all Verbal Tic-using characters in the episode. And only second to Yuudachi's "Poi~" throughout the entirety of the anime.
Zekamashi, one of the fan nicknames for Shimakaze, gets used by Kongou in episode 4.note It comes from how her name is written on her gun cannons, with the hiragana going right to left as was common at the time.
Raiden, a fan nickname for Inazuma and Ikazuchi, also gets used, again care of Kongou in episode 6.
Nagato displaying a much less serious, far more cutesy and goofy side while in private, as shown in episode 8. Mutsu even teases her about it at the end of the episode.
After Haruna's second remodel had her with dazzle camouflage, some fans started joking that she wears striped panties. Cue official art confirming that yes, she does.
Originally intended to be a niche game catering mostly to the military otaku population with a modest budget and minimal advertisement, its popularity experienced a huge surge after its players (including, among others, KohtaHirano, whose Heroic BSOD on Twitter is most commonly cited as the main reason for the popularity surge) spread the word on Twitter and/or Pixiv.
Kisaragi's appearance in the anime and being sunk in episode 3 has resulted in loads of fan artwork of just her, when before she mostly showed up in group artwork or as a background character.
The series overlaps quite well with Arpeggio of Blue Steel, despite the latter being a much older series, due to their shared reference pool of World War 2 IJN warships.
There's also frequent crossover fanart with Touken Ranbu, since both games were made by the same company and hosted on the same website, not to mention that most people consider Touken Ranbu to be Kantai Collection's Spear Counterpart.
On a more individual level, there's a fair amount of fanart pairing(in one way or another) Nagato with Godzilla. Not as surprising as you may think.note IJN Nagato was used as a target for atomic tests after the war, and actually survived the first nuke.
Creator Thumbprint: Several artists use recurrent design elements for their characters, even if they are otherwise very different from one another.
Shizuma Yoshinori (Nagato, Yamato, Shimakaze, Yukikaze...): Almost every shipgirl drawn by him wears distinctive "Rudder Stiletto" high-heel shoes. The only one with a significantly different shoe design is Akitsushima and they are rudder wedges rather than the usual stilettos. He also has a thing about sentient turrets, demonstrated with the Rensouhous and the Long 10cm-chan. Coincidentally, all but two of his ship girls feature exceptional stats. The Yamato-class need little introduction. The Nagato-class were the strongest battleships available before the Yamato-class appeared and Power Creep kicked in. Shimakaze and Yukikaze have maximum stats on par with destroyers who have second remodels, Amatsukaze has excellent durability and evasion and the Akizuki-class have tremendous Anti-Air. Iowa is only second to Yamato-class in firepower and armor, while having superlative LOS and AA...as a fast battleship. Only Tokitsukaze features generic Kagerou-class stats, while Akitsushima compensates for her poor stats with her unique gear (A sentient Flying Boat).
Ayaki (Tenryuu, Murakumo, Nenohi...): Every ship girl drawn by this artist wear some form of Floating Headgear. Additionally, all but one of them wear bladed anklets in their unremodelled form.
Shibafu (Fubuki-class, Kitakami, Mogami, Ise-class, Akagi, several others...): Unfortunately, the shipgirls drawn by him only feature the same few faces or so as well as relatively Boring but Practical designs. He compensates this with consistent art as well as the tendency for some of his shipgirls to be obsessed with being fitted planes, even discounting his Aircraft Carriers.
Kuuro Kuro (Nagara-class, Ryuujou, Hiyou, Akitsu maru): His shipgirls are usually Shinto-themed. His Nagara-class feature Shide and all but two of his Aircraft Carriers are Onmyouji. Only his IJA shipgirls are removed from this theme. Akitsu Maru ends up being a Buddhist-styled Onmyouji and Maruyu is as removed from the theme as it is possible.
Bob: His shipgirls are Colour-Coded for Your Convenience as he usually draws whole classes. The Tone-class (2 girls) are Green, the Sendai-class (3 girls) are Orange and the Myoukou-class (4 girls) are Purple. Shouhou is his only shipgirl who is "alone". Zuihou, part of the same class, is drawn by another artist.
Development Hell: Kancolle Kai was originally scheduled to be released sometime in 2014. Then it was pushed back to spring 2015. Then to November 26, 2015. Then to February 18, 2016. To add insult to injury, the final delay was announced one month before the scheduled release. While it was finally released in February 2016, many fans fear that the repeated delays have hurt the game's chances. That worry turned out to be unnecessary, as the franchise's sheer popularity have made up for its shortcoming well enough to becoming one of the top-selling PS Vita game at its release.
Fandom Nickname: Players are referred to as admirals. Unsurprisingly, given the game's premise.
New players are sometimes called newfaces or newface admirals, from one of Kongou's Engrish lines.
Follow the Leader: Warship Girls is Chinese game for the Android with a similar premise like Kantai Collection. However, unlike Kantai Collection which features mostly WW2 IJN warships, Warship Girls features WW2 Warships from all sides of the War, and is also slated for an English release, which debuted at E3 2015.
Irony as She Is Cast: Sumire Uesaka is well known as a Russophile, yet the role of Verniy was given to Aya Suzaki. The official 4koma has Fubuki (whom Sumire Uesaka voices) communicating with the suddenly converted Verniy (Hibiki's second remodel) with (supposedly) good Russian, only to reveal that Verniy cannot really speak Russian apart from rudimentary words.
Played With in the official 4koma. One possible reason why Fubuki is able to speak fluent Russian (as mentioned in the Irony as She Is Cast above) is because a previous incarnation of Fubuki (a Harusame-class destroyer) was active during the Russo-Japanese War.
Amagi shares her name with the unfinished and ultimately scrapped battlecruiser Amagi, who was historically Akagi's sister ship. Some fanartists portray Akagi fawning over Amagi as a result of that, while in 4koma it goes with 'confusing linage' gagNote Unryuu-class girls are technically Hiryuu's children, and it was previously noted that Akagi and Hiryuu are cousins..
No Export for You: The only way to play the game is to register on the Japanese-language segment of the DMM website, which itself is inaccessible to non-Japanese IP addresses. This means to even register for the game, a prospective non-Japanese player will have to jump through a lot of hoops to do so (usually by using VPN), never mind getting to play the game, which then requires newly registered members to win a lottery for one of the limited slots per server. And competition is steep for server slots.
The January 29, 2014 update was a rude awakening for many foreign players, as the most prevalent method used to play the game (the API link) no longer worked, since DMM had the game purge its API lists every 90 minutes. This meant that anyone who wanted to play via API was now essentially playing on a timer, and they had to hop on VPN to renew their API link when the time was "up". The other choices were playing on the VPN full-time, which carried its own associated risk, mainly a chance of getting banned for using a single IP (as DMM would technically see a single IP used by multiple accounts), or purchasing a private VPN to play the game on. In any case, this caused a lot of grief for non-Japanese players, causing some of them to drop the game outright rather than face the hassle of renewing every hour and a half. However, said API renewal forced a lot of players to log in simultaneously, overloading DMM's log-in servers, and essentially making the game inaccessible to everyone for hours on end. It was quietly removed in a subsequent update.
However, API links is no longer a concern. A not-so-recent method involving cookie editing allows any foreign player to play the game properly.
Since Koreans hate this game, the anime series is not available on Koreanote Aniplus, a Korea-based TV channel, release Kancolle anime only in Singapore and Indonesia and not in their own country.. It isn't available in China, Taiwan, Hong Kong. Merchandise from this game isn't available in those countries, too.
However, in Singapore, one of the many territories that suffered greatly under Imperial Japan, merchandise and Cosplay of the ship girls are popular.
Promoted Fanboy: Jiji, the artist for the Italian ships, has done fanart of the game before. Just don't look for it at work.
When the Shoukaku sisters were given their second remodels, the developers promised they would be able to operate jet aircraft. To further the hype, the Ne Type Engine was released as part of the November 2015 ranking rewards. Now, eight months later, there are still no jets available.
Shrug of God: The developers are ridiculously closed-lipped about the origins of both the player-controlled fleet girls and their opponents, the Abyssal Fleet, which leads not only to fans making their own theories, but even to the official print spinoffs not agreeing on where they came from.
Sleeper Hit: The game was originally meant for the very niche market of military otaku, but thanks to some Colbert Bumps from big names in the manga and anime industries (the most notable example being Kohta Hirano's epic meltdowns about the game on Twitter) it got a lot more popular than intended.
The temporarily playable Fleet of Fog ships. Let's just say, if the marriage(temp) system, which was confirmed for eventual implementation before the Arpeggio event started (and was eventually implemented some time after it ended), with the concept for it being leaked out some time before that, had instead been implemented before the event started...