In my personal opinion, Mem cakes are some of the most fascinating things the octo expansion gave us lore wise. They were fun little collectibles, but also make you want to think about their purpose and what they mean.
And, as tough as it was, I completed every station in the DLC to get every mem cake. (Still haven't beaten inner agent 3 yet 😔 but she's a whole other can of worms that I'll get into another time)
We're not gonna go into super detail over ALL of them and their poems today (unless you guys want that!) but just the ones that seem important enough to discuss right now.
What we already know
It's stated by C.Q. Cumber, as well as the splatoon wiki, that mem cakes are physical manifestations of agent 8's lost memories. You get them by completing a stage in the deep sea metro. However this raises.. lots of questions. For starters some of these mem cakes are surface things that agent 8 shouldn't have known about? Like salmonid, or pearl, or the shop keepers, or the clothing brands. And that's not even all the things she shouldn't know about!
Going off what we already know, out of the 80 mem cakes 8 should reasonably only have lost memories of around 38 mem cakes. (I counted the ones)
This includes:
• the entire inkling line
• the entire octarian line
• the respawn point, the bumper, the squid bumper, and the balloons
• the entire weapon line
• marina
• the entire hero mode line
First, a short explanation on why these make sense for 8 to have memories of. If you wish to skip this segment the next will start in bolded letters
The entire inkling line = inklings are the main enemy of the Octarians so it makes sense every octarian would know about them. The mem cake description of the first one makes the most sense as it depicts 8's conflicted feelings on not wanting to fight inklings. the other 4 make most sense to depict a turf war but for 8's sake it might make more sense for these memories to be off the stories of the great turf war against the inklings.
The entire octarian line = do I need to explain this one? I feel like I don't need to explain this one.
the respawn point, the bumper, the squid bumper, and the balloons = these are all items that can be found in the sections of hero mode, so we can assume 8 would have seen them.
The entire weapon line = octarians can use a variety of weapons and have seen inklings use weapons from the great turf war so, again we can assume 8 has seen or heard of them
Marina = marina, from her file in the chat rooms, seems to have had an important role in Octarian society before she left. Being so high up in the hierarchy, it just makes sense 8 would know of her
The entire hero mode line = octavio is obvious. He's the king, of course she'd know him. Marie and Callie freed the octarians the first time, but this actually tells us WHEN agent 8 was freed. Or rather when she did leave. It wasn't during splatoon 1, but splatoon 2's hero mode. Why? Because her mem cake of Callie is when she was brain washed, and Marie has her kimono on. The octarians stole the scrolls and the sardinium so she would of seen them around, same with the keys. The zapfish and power eggs play a huge role with the octarians so it'd be obvious she'd have memories of them too.
Explanations
There is one excuse we can use for the memories that there aren't an explanation for. But the thing is, it's a dumb excuse that could be used for everything and splatoon doesn't have that kind of lazy writing. But it does work for SOME things so we can use it for a few.
Some of the mem cakes are 8's memories she's making as she goes through with stuff the captain, marina, and pearl are telling her.
Let's get out of the way the ones this can be used for.
Pearl. Agent Eight first meets pearl in the deep sea metro rather early on, and quickly becomes an important person in the octoling's life. It'd make sense that the memories would form into a mem cake.
Ranked Modes and Trees. Looking at the chat rooms you can see multiple instances of pearl and marina talking about the surface to 8. So I think it'd make sense that over the radio or something, they'd tell them about the plant life above ground (especially marina since I think she'd want someone to know what that's like instead of taking it all in full force like she had to) and the different turf modes to get 8 more excited. This one is more of a stretch though, and it's possible this could also be premade memories from inkling history lessons underground to get a feel for the surface when the octarians planned to take it over?
Shop keepers + The Judds + Mr Grizz. It's a lazy excuse we're using for so many but it's all I can think of to say pearl marina and the captain told 8 about these people too. There's just no way I can think of that she'd already have memories of them before the metro.
(I wanna point out Mr Grizz's mem cake. I feel so bad for 8 because in the Poem of that one: oh what I'd give to be employed! Better, I'd say, to work for pay, than ride this subway through the void" it implies that she'd honestly rather be out there risking her back for a greedy radio then go through this hell and I just want to hug her so badly)
Now, that just leaves a few sections of mem cakes left.
The salmonids, the clothing brands, and the clothing.
The salmonid memories, this one is a huge stretch as we're using some lore that might not be canon?
The splatoon manga is not one people tend to read since it's more marketed towards younger audiences. However, in one of the series when the characters Goggles, Mask, Emperor, and Gloves go to work a salmon run shift, goggles falls into the water on the boat ride back to inkopolis. See the thing about this is that he doesn't just get splatted, he falls into the deep sea metro.
Now, this is confusing for so many reasons?? Because in the chat logs marina states the deep sea metro and kamabo co seem to be somewhere like a whole new dimension from inkopolis, so saying it's just under the waters of the salmon territory seems too simplified. I wanna go into this more on its own one day.
However, as much as the manga lore branches from the game lore, it gives a reasonable explanation on how 8 knows about salmonid. It's highly possible kamabo co purposely made their facility underneath the salmonid ocean so they could purposely fall in and experiment on them. The beginning where you chose an octoling very much hints that 8 was in that testing lab before she lost her memories, and could have seen different salmon in there. Again that's something I want to go on about another time.
The clothing brand one connects with the clothes. Humans tend to throw trash in the ocean, and sometimes trash that isn't intended to go into the ocean ends up there anyway. It is highly possible old clothing items end up in the ocean and down the same way goggles and (possibly) the salmonid do. Or, the trash ends up underground, and maybe 8 in the past has found old inkling clothes lying around, and has seen the branding on them.
Evidence for the clothes underground are with the poems, like how 8 says with the skalop hoodie "it's too frigid to be exposed!" Which could relate to the exposing octarian armor. The neon sea slugs shoes has part of the poem that describes finding these shoes as "a stroke of luck" which could hint how clothes don't seem too common underground.
Now, this next part is short. How do the mem cakes bring memories back?
Simply put I think you eat them. They're called "mem(ory) cakes" for a reason. They're consumable memories! How that works scientifically? Ehhhh maybe I'll research that another time.
What's more curious is how come they form in the test chambers? My theory is that it has to do with the idea that 8 was at kamabo before losing her memories, and the mem cakes are part of their experiments. This is getting too long though, so I'll revisit that idea another time. Gotta save stuff to talk about in other chapters after all!!
So what did you guys think? Got any theories of your own? Any ideas for future theories, or any characters you want my headcanons of? Let me know below!
Stay fresh everyone :)