Ensemble Dark Horse / Azur Lane

• The absolute biggest has got to be Unicorn. On the surface she's just a generic imouto character, right? And yet, on most image sites and whatnot, you'll find more fanart or fanworks featuring her than the grand total that some minor factions have. This is due largely to her gameplay: she's one of the only healing units in the entire game, healing the fleet for up to 8% of their total HP every time she launches an airstrike, and she improves the whole fleet's reload speed. Combine this with the fact that she can be farmed comparatively early in the game (chapters 4-4 and 5-4), and she's by far the most popular healer in the entire game and one of the most beloved members of the roster. She placed highly on the original 2017 polls and is placing pretty well in the 2019 ones (more China and Japan than the English server). This is in spite of word that her oath skin is indeed on the way during the polls (she finally got one in 2020)
  • Her retrofit officially making her the best healing ship in the game and one of the best mob-clearing aircraft carriers in the game only made her popularity skyrocket all over again.
• Laffey; the drunk sleepy Destroyer has been a low key favorite scoring well in the original polls and is ranking quite well in the 2019 ones (with her being first in China's qualifiers); this is in spite of word that Laffey will have an Oath skin on the way. The anime airing has only helped the impression as she's a key character in it and her moments has further endeared her to current and new fans alike. Even in Slow Ahead, she has a way of low key stealing the scene in the eyes of some.
• Vampire is another, debuting in the Plan Z event and becoming quite popular from there, getting a number of skins that was at the time only typical of Gold rarity ships, and the first Purple rarity to get a wedding skin.
• Ayanami is another; easily the most popular of the starters due to her cool sword, ability to do a rather massive torpedo damage early on, and quiet/cute demeanor. The numerous skins she proceeded to get helped (though that's due to her artist not having to do a massive workload unlike the other three's who share one), one of which is a wedding skin, making her the second purple rarity ship to do so.
• And there's Yamashiro, whose mix of cute ditziness, paw posing, and sideboob endeared her to a number of players and the decent number of free skins only helped. She's also the only Blue (Rare) rarity ship to have an oath skin. In contrast, her sister Fusou is only just starting to get some paid skins. She does run into a bit of the same backlash that Cygnet gets, and may ramp up as of October 2019, she has 7 skins total besides base and refit with the new schoolgirl outfit and currently Taiwan version only Beach (not swimsuit) skin. That is more than even the most popular Gold(Super Rare/SSR) ships.
• Graf Spee is incredibly popular in Japan, who now boasts 3 extra skins other than her default one. Not bad for a ship that was barely introduced a year ago.
• In Japan, Baltimore quickly reached the top 5 (in qualifier rounds) in the 2019 in-game popularity poll event, despite the fact that she's one of the newest ships in the game at that point. It probably helps by the fact that her "After-School Ace" skin is incredibly popular among fan artists. And Japan may also like the Kamen Rider references present in her lines and design. Her base skin being attractive, stylish yet not being excessive mixed with her earnest personality doesn't hurt either. It's such that she got another skin when another event ran.
• Amagi quickly rose to the top of the 2019 EN in-game popularity poll (also in the qualifier rounds), easily beating out the likes of Enterprise, Taihou, and Bismarck for the top spot. Reasons being sympathy for her back story, her demure, kind yet mischievous personality, effective skill kit, and gorgeous yet clean design by Liduke. Bismarck is also pretty popular for similar reasons. It's to the point where her swimsuit skin was added on EN's 2nd anniversary and is a timed exclusive and before that she got a server named after her.
• Bache has gained a sudden and to some of the western fanbase, unexpected skin during the collaboration with Yamaha (but not part of it specifically) which turned out to be even more over-the-top than her base skin. This seems to be a mix of her being very popular in Japan and Yostar trying to curry favor with her artist (who did Girls Frontline stuff in the past) since he favors such "unique" designs as this.
• A Rule 34 centric example is how fanart for Bremerton exploded once her tennis skin was revealed, especially when compared to the smaller amount of Rule 34 or fan art in general of her default look. The fact that it highlights her voluptuous body alongside it being easy material for Going Commando and Theiss Titillation Theory provided a new form of fanservice to experiment with as opposed to the usual kimono and bikini fare. Fans were quick to note how much Bremerton overshadowed other ships revealed at the same time like Intrepid thanks to her skin and teasing Ms. Fanservice demeanor in general. The developers clearly loved the attention the skin received and made one of the official loading screens an upshot of Bremerton's tennis skirt and top, going with the fan popular braless take.
  • Zara and Honolulu's popularity also exploded for similar reasons with their swimsuit skins, but Bremerton's addition gave the fandom a new Power Trio of "Ms. Fanservice twintailed redheads" to draw together. The fact that each of them deals with the Commander and his flirting in a different way makes them popular foils for each other, with Zara being the elegant Shameless Fanservice Girl, Bremerton being the chirpy Innocent Fanservice Girl and Honolulu being a tsundere Reluctant Fanservice Girl.
• For the exact same reasons as Bremerton, St. Louis got a renewal (she was rather popular to begin with) in popularity once her Luxurious Wheels skin was revealed, with her being in a Cool Car and very revealing dress with a possible boost to her already great figure. Dress might even be a generous description for it, and as with Bremerton's tennis outfit, the Going Commando and Theiss Titillation Theory fetish the dress provided gave fans another source of unconventional fetish fuel for Rule 34. Her Luxurious Wheels skin has thus been a source for a lot of cosplay and disproportionate amount of fan art for her. And just to conclude on St. Louis' rise to fame mirroring Bremerton's, the developers also made her in her Luxurious Wheels skin a loading screen◊ with a pose that highlights her legs.
• Pamiat Merkuria from the Northern Overture event caught on with a number of fans, due to the combination of shortstack frame, cheeky yet cute attitude. She was picked as the character to feature in the Slow Ahead manga over higher rarity ships. And it's telling that during the japanese third anniversary event, she got a section which revealed she got a 3d model, something usually reserved for some of Kincora's popular ships (Sirius, Le Malin, and Dido) with two of them being DLC characters in Crosswave. She also has a series of videos with the same 3d model doing previews of the next episode of the Slow Ahead anime.
  • Culminated in her receiving a retrofit (an increasingly rare occurrence in modern AL) in the second Russian-focused event, Khorovod of Dawn's Rhime. This is despite her being a limited ship from the first Russian event that has not yet been given a rerun, meaning that if you don't already have her, it is impossible to obtain her to utilize said retrofit any time in the near future. It helps her carry her own weight offensive at the very least, a big improvement from her stats before (where she could do a decent job tanking... and that's it)
• Biloxi has made an impression during the Lunar New year 2020 banner to varying degrees to the point where the following Anniversary in China gave her a formal skin which highlighted the her tomboyish appeal (For reference, it was at this point the banner's big star Dido got her first and only skin). And then come late December 2020/early January 2021 gave her a New Years' skin that solely played up her feminine traits and more surprisingly, sneakily added her into Inverted Orthant's event pool without a rate up. While it was the Chinese that caused this, the EN playerbase certainly likes her.
• As far as Sirens go, Purifier was already fairly popular with the fanbase. Her popularity skyrocketed, however, to point where she’s easily the most popular of the named Siren characters (unless you count G), following the hololive collab event and especially the SSSS.GRIDMAN / SSSS.DYNɅZENON collab event, mostly because of her ‘Purity’ persona. Following the latter collab event, the Azur Lane Subreddit was practically flooded with threads and memes demanding she be Promoted to Playable. The ending of the latter event distinctly left open the possibility that this could actually happen via an Ambiguous Situation concerning Purity’s ultimate fate.
• Elbe from the Tower of Transcendence event proved to be a surprising hit, being a purple rarity CVL of mild effectiveness. The combination of art, her smug ojou-ish demeanor, and ineffectual "bad girl" attitude endeared her to many, arguably more so than Prinz Adalbert, a higher rarity ship.