Diablo’s obsession with Rimuru might seem strange at first. After all, Diablo was one of the oldest and most powerful demons in the world, while Rimuru was initially nothing more than a newly reincarnated slime.
So why did a Primordial Demon like Diablo become so fascinated with him?
The answer went back to something Diablo encountered long before he ever became Rimuru’s subordinate: Shizue Izawa’s mysterious anti-magic mask.
How Did Diablo First Encounter Shizue?
Long before he became Rimuru’s servant, Diablo was known as Noir, the Primordial Black.
Unlike many other powerful beings, Noir wasn’t particularly interested in pursuing greater strength.
His overwhelming power had already made most battles uninteresting to him, so he instead followed his own curiosity and whims.
One day, Noir answered a demon summoning performed by a member of the Silver Wings. The woman had summoned him to take revenge on the demons controlling the Nation of Filtwood.
While carrying out his task, Noir encountered Shizue Izawa.
Shizue stood in his way, and Noir decided to eliminate her before continuing with his objective.
But then something completely unexpected happened.
Why Did Shizue’s Mask Shock Diablo?
When Diablo attacked Shizue, her anti-magic mask repelled his attack with such force that it blew away his arm.
This was something impossible, and Diablo couldn’t understand.
Shizue was merely a human, yet the mask she wore had resisted the attack of a Primordial Demon.
The mask wasn’t simply durable, it possessed properties that seemed to transcend the normal rules of magic.
That moment completely changed Diablo’s interest.
He wasn’t fascinated by Shizue because she was exceptionally powerful. Instead, he became fascinated by the mask she possessed.
For Diablo, the mask represented exactly the kind of phenomenon that could challenge his understanding of the world’s rules.
Why Did Diablo Continue Watching Shizue?
After his encounter with Shizue, Diablo returned to the Daemon Realm but continued observing her from afar.
He wanted to understand the mysterious mask.
What was it?
Why could it resist his attack?
And more importantly, why did it possess properties that seemed impossible even to a Primordial Demon?
Diablo continued monitoring Shizue and the mask for years, but he never discovered its true nature.
The mystery remained unresolved until Shizue eventually died.
How Did the Mask End Up in Rimuru’s Hands?
Before her death, Shizue entrusted the mask to Rimuru.
Rimuru initially had no reason to suspect that the mask was anything extraordinary.
To him, it was simply an important object that had belonged to Shizue.
But the mask had a much stranger history than Rimuru realized.
It was caught inside a time loop involving Chloe and Chronoa.
The mask passed through the sequence of Chloe/Chronoa → Shizue → Rimuru → Chloe/Chronoa, meaning the same object was repeatedly carried through time.
And this was where the mask became a genuine paradox.
Why Was the Mask a Paradox?
The mask had no ordinary beginning in the timeline.
Rimuru gave the mask to Chloe, Chloe later traveled through time into the past carrying the mask with her and eventually gave it to Shizue, Shizue then passed it to Rimuru, completing the loop.
This meant the same mask existed in a cycle where it was passed from Rimuru to Chloe, then back to Shizue, and finally to Rimuru again.
So the same mask continued to pass through the time loop.
But where did it originally come from?
That was the strange part.
The mask was ultimately identified as being created by Rimuru.
However, because Chloe carried the same mask back into the past, it eventually reached Rimuru, creating a paradox where the mask had already existed before its creator had created it.
The exact point of Rimuru’s creation of the mask was obscured by the countless time loops, leaving its true point of origin impossible to determine.
In other words, the mask existed as part of a closed causal cycle rather than having a clear beginning or origin.
This paradoxical existence was what made the mask such a world-breaking object, it defied the normal relationship between cause and effect.
That strange relationship between creation and causality was exactly the sort of phenomenon that fascinated Diablo.
Why Did the Mask Cracking in Rimuru’s Possession Change Everything?
This was the moment that completely redirected Diablo’s attention.
The mask had previously been effectively indestructible before coming into contact with Rimuru because of the way it was bound by cause and effect.
Even Diablo’s attack had been repelled by it.
Yet when the mask eventually came into Rimuru’s possession, it cracked and lost its special properties.
Diablo witnessed this.
And suddenly, the mystery he’d been observing for years had a new piece of information.
The mask was a world-breaking object, yet it cracked in Rimuru’s possession!
That meant that Rimuru himself was even more broken.
This was what led Diablo to conclude that Rimuru was somehow connected to the mask’s existence.
While Rimuru had no idea about the mask’s special properties and why such a powerful demon was simping for him!
Why Did Diablo Become Obsessed With Rimuru?
At this point, Diablo’s obsession shifted from the mask to the person connected to it.
For years, he had been trying to understand an object that appeared to transcend ordinary rules of time and causality.
Then that object ended up in Rimuru’s hands and reacted to him in a way that revealed a connection between Rimuru and its existence.
To Diablo, this wasn’t simply evidence that Rimuru was powerful.
It meant that Rimuru was connected to a phenomenon that surpassed his understanding of the world’s rules.
And this was exactly what made Rimuru so fascinating to him.
Diablo was not initially interested in Rimuru because Rimuru was stronger than him.
In fact, when their paths first crossed, Rimuru was nowhere near Diablo’s level.
What attracted Diablo was the mystery surrounding Rimuru.
The mask had led him to Rimuru, and Rimuru had become the key to the mystery that Diablo had been unable to solve.
This is also why Diablo later regarded Rimuru as connected to the truth of the world.
His fascination wasn’t merely about power, it was about discovering something beyond the ordinary laws of the world.
Did Diablo’s Curiosity Eventually Become Loyalty?
This was what made Diablo’s relationship with Rimuru so unusual.
At first, Diablo’s interest was essentially intellectual curiosity, he had encountered something he couldn’t understand and wanted to know more.
But after watching Rimuru’s growth, his curiosity gradually transformed into admiration and eventually absolute devotion.
Rimuru repeatedly accomplished things that shouldn’t have been possible for an ordinary existence. He continued evolving, gained enormous influence, and eventually became a True Demon Lord.
For Diablo, every one of these developments gave him another reason to remain fascinated with Rimuru.
The mystery never disappeared.
It only became deeper.
And eventually, Diablo no longer wanted merely to observe Rimuru, he wanted to serve him.
Diablo’s devotion to Rimuru was also demonstrated when Diablo recruited the Demoness Trio.
Read How Diablo Recruited the Demoness Trio for the full explanation.
Final Thoughts
Diablo’s obsession with Rimuru didn’t actually begin with Rimuru.
It began with Shizue’s mask.
Diablo encountered an object that could repel the attack of a Primordial Demon, something that appeared to violate the rules of magic and causality. He spent years observing Shizue and trying to understand it.
Then the mask reached Rimuru.
And when it cracked in Rimuru’s possession, Diablo finally discovered the connection he’d been looking for: Rimuru was the source of the mask’s existence.
That was the moment the mask stopped being Diablo’s greatest mystery.
Rimuru became the mystery.
And for a being who had spent his existence searching for something capable of breaking the rules of the world, discovering Rimuru was far more fascinating than discovering the answer to the mask ever could have been.
The mask was what caught Diablo’s attention… But Rimuru was what captured it forever.
