- Certain punny slang and profanity is widespread amongst fans. For example, Inklings saying "squit" instead of "shit," or both Inklings and Octolings alike using Cod in place of, well, God.
- Might actually be canon, as during Splatoon 2's story mode, there are a few instances where Marie exclaims "Oh, carp!" when, despite being text, the implication is Oh, Crap!.
- Considering that Inklings are evolved squid, they're generally viewed as laying eggs. Octolings, Jellyfish, and the other species are the same way. Canonically, while nothing as been said about most of these species, the Jellyfish reproduce via asexual reproduction.
- It is commonly believed by fans that the Octolings are the base species for the Octarians as a whole, possessing a sexual reproduction and a development cycle similar to the Inklings while the Octotrooper classes are created from tentacles cut off from Octolings and thus have no reproductive capacity. The official artbook guides don't give a clear answer on whether Octolings are uniquely different from the Octotroopers or if they are just advanced troopers born from cut-off tentacles. One artwork does seem to indicate an Octoling can be developed from a severed tentacle, but PAUL the 10-year old Octoling DJ looks like an Octoling version of a prepubescent Inkling.
- It was assumed by fans throughout the original Splatoon that the characters were much smaller than adult humans. The reveal of character heights in supplementary material of the second game, however, reveals that everyone is to human scale.
- The violinist of Bottom Feeders is feminine looking but looks like a male Betta fish. Fan consensus is that they're either a effeminate looking male or a transgender person.
- "Inktolings" are a common subject in fan art, the hybrid offsprings of an Inkling and Octoling. Many fans want this idea to be official canon as it would finalize the unity of Inkling and Octoling community after a century-long feud.
- Agent 3 having scarring or discoloration on half of their face and part of their tentacles/hair because of Commander Tartar's brainwashing is a common headcanon in fanart. As the Captain in Splatoon 3, they actually do have scars on the tips of their hair.
- Another headcanon is that the original Agent 3, Agent 4, Agent 8 and New Agent 3 are female, mainly due to the female versions (the default female Inkling in New Agent 3's case) being featured prominently in promotional material. This is seemingly confirmed in the case of the original Agent 3, as their default appearance in later games is always that of the Splatoon 1 female Inkling (though Gender-Neutral Writing is naturally still used).
- Many fan artists gave Cap'n Cuttlefish's squid form his signature beard, something Splatoon 3 would later confirm he actually has.
- The Smallfry affiliated with the player in Splatoon 3's campaign is often called "Little Buddy" or "Lil' Buddy" after their nickname in the player customization menu, in order to distinguish them from other Smallfries.
- Harmony's off demeanor is sometimes interpreted as her being The Stoner, or being on the autism spectrum.
- It's a somewhat common trend to depict some Inklings keeping Super Sea Snails as pets, even though the game implies that all they are used for is rewards for Splatfests.
- It's implied that Callie and Marie were 17-18 during the events of the first game, but most interpret them as having been in their early 20s instead.
- More than a few fan works portray Callie and Marie as adopted siblings due to the fact they're biologically cousins yet their idol duo is named "Squid Sisters." This is usually in conjunction with them being raised by their grandfather. This was jossed in Squid Sisters Stories, as Marie visits her folks in Chapter 5. Callie also has a chance of mentioning her own parents when spoken to after completing Splatoon 2's Hero Mode.
Off the Hook
- Most fans agree that Marina and Pearl live together, and this is often in conjunction with them also being a couple, based on the romantic undertones in some of Marina's dialogue; especially in Japanese, where she more regularly shows admiration towards Pearl and her official character biography describes her as a "maiden in love". While nothing official has been said on their relationship, the interview included with the Japanese Octotune soundtrack jossed the roommates theory, though it's implied Marina regularly stays Pearl's house regardless.
- Before the Octo Expansion, Western fans generally assumed that everyone knew Marina was an Octoling and that (most) didn't care. In canon, few people outside of the New Squidbeak Splatoon are familiar enough with Octarians to recognize that she was one, and so think that she is an "exotic" looking Inkling. This even extended to Pearl in the original Japanese; the English localization didn't get that memo, and so Pearl had already alluded to knowing on multiple occasions before that point. The team's fix for this was for Pearl to make Marina's ex-military status the real surprise for her, while she already knew Marina as an Octoling, but didn't know how to broach the subject. A fair number of Western fic writers would end up running with the idea of Pearl being a Secret Secret-Keeper as a result.
- Pearl's short height, immature personality, and unusual design (including a single pointed tooth, only seen in prepubescent Inklings) initially caused a lot of fans to theorize that she was Younger than They Look. This was eventually jossed when she was given a canon age of 21, pinning her as the older between the Off the Hook duo. Pearl's height is intended as a reference to the Northern Pygmy Squid.
- Pearl as a Sir Swears-a-Lot due to her tough personality and her career as a rapper. In an odd turn of events for a Nintendo game, the Octo Expansion confirmed this by introducing one of her old songs before she and Marina formed Off the Hook, "#$@%* Dudes Be #$@%* Sleepin". The song is a faced-paced heavy metal Cluster F-Bomb, with a prolonged Sound-Effect Bleep on top of it all. The hidden bonus track on one of the soundtracks also has Pearl seemingly swearing after flubbing a recording.
- As Pearl's full name is only revealed in the original Japanese (where she is Hime Houzuki), fanon has taken to using Houzuki as her last name in English as well.
- SashiMori's backstory makes mention of them previously being a death metal group, before ousting their tyrannical lead singer and eventually replacing them with DJ PAUL. Given Pearl's personality, history as a death metal vocalist, and it being stated that one band member's shell was a asset in dealing with their singer's harsh vocals, it is assumed their old leader was Pearl.
- Marina is seen as having a Dark and Troubled Past as a high ranking ex-soldier for the Octarian army who escaped to the surface. Canon would later confirm that while she was part of the army, she was an engineer rather than a soldier. Fanon also depicts Marina as having grown up poor, in contrast to her wealthy best friend Pearl and as part of the wider fanon of Octolings living in destitute conditions in comparison to the more carefree Inklings.
- Marina as bilingual and speaking with an accent. This comes from the Japanese version, where her speech is occasionally rendered in katakana, which is used by other Octarian characters to indicate that they are speaking a different language. Her ordinary speech is only partially rendered this way, implying an accent of some sort, while her lyrics in Off the Hook's music are entirely in katakana, which indicates that she's singing in Octarian. Likewise, her speech in the Japanese version is often overly formal, and she tends to make many malapropisms, further indicating that she's only recently learned the Inkling language; Western fans drop that latter bit unless writing about when she first came to the surface though, sticking to just making her overly polite.
- Early on, Marina was theorized to be directly related to DJ Octavio, as the two are both Octarian DJs and were the only named Octarian characters in the series for quite some time. In canon, while Marina was a high-ranking officer serving under Octavio, her backstory makes no mention of any relation to him. Furthermore, DJing doesn't seem to be all that uncommon among Octarians, as we later saw in artists like Dedf1sh, SashiMori's PAUL, and Diss-Pair's Warabi.
- To reconcile her Japanese and international personalities, many Western fans decided Marina was a Shrinking Violet who only acted sarcastic and sassy while on-air to compensate for how nervous she really felt as an Octoling integrating into Inkling society. The Octo Expansion would go on to confirm that this is almost exactly the case.
- Although officially confirmed to be female, Shiver is often depicted by fans as being a non-binary Octoling who uses both she/her and they/them pronouns, or is assigned female-at-birth.
- If Frye and Shiver are getting shipped together, expect to see Big Man as the duo's biggest Shipper on Deck.