CB Theory: Aku Aku’s Guardianship (and the Brothers’ Human Past)
Out of all the characters in the Crash Bandicoot series, I've always found myself drawn towards Aku Aku and Uka Uka respectively. Not only for their unique designs, characterization, and outright whimsical concept (the spirits of two recognized witch doctors immortalized through floating wooden masks? Sign me up!) - but also for the possibilities their characters open up within the franchise's lore.
Below would be one of those possibilities that I like to theorize about; the very reason why Aku Aku devotes himself to protecting our little orange marsupial alongside the archipelago they reside in.
As a disclaimer, I'd like to state that what I'm about to describe will all be grounded in fiction (we're talking about a denim pants-wearing bandicoot around here) and are purely on headcanon territory. I'll be tackling some massive "what if" scenarios that have little to no evidence canonically but are fun to think of personally.
With that out of the way, allow me to go on a full-on I'm-desperate-for-more-lore-and-overall-content-of-these-masks-and-therefore-I'm-making-this-up-as-I-go-to-satisfy-those-needs ramble.
Let's start with Aku Aku. He's a being of high intellect, for sure - usually filling in the role of an advisor to the rest of the characters when they find themselves faced with tricky situations. This aspect of his could only be rivaled by his power, as he not only grants protection to other beings when summoned but has also shown the capability of sealing other mystical entities (such as his brother) away when he sensed that the world would be in peril otherwise.
So with these in mind, why in the world would he go and devote his guardianship role to Crash? The dude's another failed animal experiment from none other than Dr. Cortex; someone who had been planning a worldwide takeover for god-knows how long. Surely with how ancient Aku Aku is portrayed to be, he would have some previous experience encountering Cortex's other specimens (Ripper Roo, Dingodile, Pinstripe- you name that boss battle) and know of how dangerous they are. Heck, Crash himself is unpredictable right from the get-go. His life cycle had only just started by the time he had washed up on the beach and his first-ever conscious decisions are to flail around, breaking boxes and any enemies that happen to cross his path. Sure, he has a good heart. That's something that we come to know throughout the game, as he actively goes out of his way to choose the greater good and stop Cortex from fulfilling his evil plots. But something like that requires the luxury of time that Aku Aku didn't have when Crash decided to spin right into one of his crates on that fateful day.
So what was Aku Aku's thought process upon meeting the bandicoot and deciding to be his protector?
I like to think that it was first out of obligation. Aku Aku's crates seemed to exist alongside the others found within the island, far before Crash had come into contact with any of them. Perhaps - when his spirit was first incarnated into the mask, he made it so that any living creature in dire need could summon him when needed (even if this proved to be a little impractical, given how rarely any of the other creatures break his boxes). So that takes care of their meeting encounter on the beachside in the first game and one could even argue that this logic stretches into the second game, given his absence from the bandicoot duo.
What I'm far more interested in would be the reason why he stays in the third game and beyond.
We're talking about an all-powerful being here who could travel anywhere in the universe in the blink of an eye (and even across universes, taking Twinsanity into account), and for whatever reason, he decides to stay with the bandicoots in their own household, watching over them even as they do something as mundane as figuring out new yoyo tricks and watching Uncharted 4 on their laptops.
To answer that, I have to take a moment to talk about an aspect in Aku Aku's life that we all barely know about: his human incarnation. He couldn't have been a magical floating mask for the entirety of his life, after all. So let's say that centuries ago, he was the witch doctor of one of the tribes on the archipelago, appointed by the chief leader to be at his side and care for the rest of their people. A powerful yet humble witch doctor, at that, as he would never abuse his power for the sake of self-gain. Let's say that - aside from his position in the tribe, he lived a relatively normal life and even had a family to care for, including his twin brother, Uka Uka, who had also been a witch doctor in their village (but we'll get to his part later down the lane).
Let's say that - one day, Aku Aku's wife bears a child. Someone to help carry on their legacy of practicing medicinal magic, ideally. But the child themselves is born with mental disabilities, ones that have shown to only worsen as they grew up. The child found it difficult to communicate properly, to control their movements outside of impulse, and with the limited resources their world was faced with at that time, no one in the tribe seemed to understand what was wrong. Aku Aku would try his hardest; trying to use his magical abilities to help the child in any way he could in hopes of "fixing" him and finding himself at a loss whenever he was unable to.
I imagine him to be the more practical of the two, wanting things done immediately even if it entails harsher, extreme means. He was matched with his twin brother in terms of their magical prowess, with the difference between them being his lack of empathy towards others. He seems like the type to charge the tribal folk with favors in exchange for his services, that coupled with his malicious demeanor being the reason why the chief hadn't appointed him as the witch doctor of the tribe despite being on par with his brother. This event struck jealousy within him, soon spiraling into an unquenchable need to knock his brother off his perch at every opportunity he got in order to show who the better between them truly was.
That child was his opportunity - because if there's one thing that Uka Uka was also good at, it's making people believe every word he said, as ill-intended as it were.
Uka Uka claimed that the child's behavior was the result of the ancients cursing their family bloodline, aligning his statements with spiritual beliefs that the people of the tribe shared. He linked the ancients' frustration to his brother, saying how they were being punished for how unworthy Aku Aku was to handle such a high-stakes position and even citing instances of the other's failures in saving lives (as he often spent too much time trying to work around the use of force and violence). He further claimed that the curse could be spread across the entire village unless the source itself was purged, that of, the child.
Aku Aku was outright against the notion, still holding onto the belief that he would one day be able to cure the young one of their problems. But it was already too late then; his brother's words had naturally stricken fear into the hearts of the rest of their people, and it was out of their own selfish greed that they pushed for the child to be executed in order to free their village from the wrath of the ancients. It came down to the point that Aku Aku found himself helpless as the chief took the matter into his own hands, having no other choice but to follow through with Uka Uka's theory in a means to appease the restless people.
This was the breaking point in the twin brothers' relationship. The grief of losing a loved one so unfairly made something snap in the witch doctor that day, the result of which being an all-out battle between the two. With how evenly-matched they were, however, the battle had only succeeded in slowing draining each other of their energy until they both reached their final breath. In was in that very breath that they had used the remainder of their powers to seal their souls away into the mask forms, allowing their spirits to live forever and their fight to continue on for the centuries to come. Aku Aku later found the redundancy in fighting and decided to lock his brother away in the temple, keeping his malice hidden away from the world (insert his speech at the beginning of Warped here. His fear of his brother's return stems from how he's well aware of the lengths Uka Uka would go to achieve ultimate power - meaning that countless of innocent lives could be lost in the process).
That brings us back to the main concern of why Aku Aku decides to stay with the bandicoots.
I'd like to imagine that, to some degree, Crash reflects some similar characteristics of that child Aku Aku lost all those years ago. From his inability to properly communicate (outside of actions and limited words and sounds) to even the childlike innocence of the mutant when looking past his chaotic exterior. He learned from his previous mistake of trying to fix the little one of his faults and found value in just being with him; accompanying him along his journey of righting Cortex's wrongs and slowly adapting to the unique way Crash acted (which could lead to why he's shown to understand Crash's gibberish throughout the years).
In doing so, Aku Aku was not only providing the world's only hero with the necessary means and power of stopping an evil scheme - but was also hoping to fulfill his role as a fatherly figure; something that he had once failed to do years ago.
TL;DR: Aku Aku decides to be Crash's guardian as the bandicoot reflects the behaviors of a son he had lost back in his human life due to Uka Uka's doings.