Why Did Yuuki Kagurazaka Kill Mariabell Rosso? The Truth Behind the Ultimate Betrayal in Tensura
If you’re a longtime fan of That Time I Got Reincarnated as a Slime, you know the series isn’t just about Rimuru building a cozy monster nation. Beneath the wholesome diplomacy and flashy battles lies a ruthless chessboard of ambition, economics, and god-tier abilities.
And for me, one of the most jaw-dropping moments in the Tensura light novel (Volume 10) wasn’t a Demon Lord awakening or an Ultimate Skill reveal — it was Yuuki Kagurazaka murdering Mariabell Rosso without hesitation.
Let’s talk about why that scene hit so hard — and why it completely redefined Yuuki as one of the smartest (and scariest) antagonists in the series.
The Perfect Puppet Act: Yuuki’s Greatest Performance
Throughout the Western Council arc, Mariabell Rosso believed she was untouchable. As the wielder of the Unique Skill Greed, she manipulated politicians, merchants, and entire nations like pieces on a financial board.
And Yuuki? He played along beautifully.
Mariabell thought she had him under control. She believed he was just another ambitious human enthralled by her power. But that was her fatal mistake.
Yuuki possesses an abnormal constitution often referred to as an Anti-Skill ability, which allows him to negate or resist certain supernatural effects. In simple terms: he was never truly controlled.
Instead, he leaned into the role.
From a fan perspective, this is what makes Yuuki terrifying. He didn’t break free dramatically. He didn’t struggle. He didn’t rebel emotionally. He just waited.
He let Mariabell believe she was the predator — when in reality, he was studying her.
Why Mariabell Had to Die
Yuuki’s betrayal wasn’t impulsive. It wasn’t revenge. It was strategy.
Mariabell wasn’t just another villain; she was a genius economist controlling the Rosso Clan and pulling strings across the Western Nations. Her ambition? Total economic domination.
That directly clashed with Yuuki’s long-term goal: reshaping the world under his own ideal structure.
Here’s why eliminating her was essential:
- She was too intelligent to control long-term
- She held influence over key financial networks
- She knew too much about Yuuki’s shadow dealings
- She could eventually expose his plans to Rimuru
And here’s the uncomfortable truth as a fan: Rimuru might have spared her.
Rimuru has a soft spot. Even for enemies. Mariabell looked like a child. And that hesitation? Yuuki understood it.
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So he removed the problem permanently.
The Power Play: From Greed to Mammon
Now we get to the real turning point.
In Tensura, skills aren’t just abilities — they’re reflections of the soul’s desire. When Yuuki killed Mariabell, something symbolic happened.
Her Unique Skill Greed didn’t just disappear.
It chose him.
And because Yuuki’s ambition was even deeper than Mariabell’s, that power evolved into an Ultimate Skill: Mammon, Lord of Greed.
Here’s a quick breakdown:
| Aspect | Mariabell Rosso | Yuuki Kagurazaka |
|---|---|---|
| Skill Level | Unique Skill: Greed | Ultimate Skill: Mammon |
| Core Desire | Economic Control | World Restructuring |
| Control Method | Financial manipulation | Direct skill & soul interference |
| Strategic Depth | High | Extremely High |
The evolution from Greed to Mammon is symbolic. Mariabell wanted wealth.
Yuuki wanted control over existence itself.
Mammon granted abilities that pushed Yuuki into the realm of Demon Lords — skill theft, life absorption, and even mental overwriting. He didn’t just inherit her power.
He perfected it.
The Emotional Impact: When Yuuki Became a True Villain
Before this moment, Yuuki felt morally gray. Suspicious? Sure. Manipulative? Definitely. But still… somewhat human.
After he stabbed Mariabell without a flicker of guilt? That was the shift.
Raphael later confirms to Rimuru that Yuuki had been acting freely the entire time. No mind control. No excuses.
That confirmation hit harder than the murder itself.
Because it meant Yuuki wasn’t reacting to circumstances.
He was orchestrating them.
As a fan, that’s when I stopped seeing him as a wildcard and started seeing him as one of Tensura’s main long-term antagonists.
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What This Changed in the Story
Mariabell’s death did more than remove a villain.
- Crippled the Rosso Clan’s leadership
- Destabilized Granbell Rosso emotionally and politically
- Cleared the Western economic sphere for new power plays
- Gave Yuuki an Ultimate Skill
- Preserved his public image
That last point is key.
Yuuki didn’t reveal himself. He didn’t expose his hand. To most of the world, he remained respectable. Cooperative. Harmless.
That’s the scariest kind of villain.
My Personal Take as a Fan
What I love about this moment in Tensura is how grounded it feels despite the supernatural scale.
This wasn’t a flashy fight scene.
It wasn’t an Ultimate Skill duel.
It was a quiet execution.
Yuuki understood something Mariabell didn’t: in a world of monsters and Demon Lords, intelligence alone isn’t enough. You need ambition without hesitation.
Mariabell was greedy.
Yuuki was ruthless.
And in Tensura, ruthlessness often wins.
Final Thoughts
Yuuki Kagurazaka killing Mariabell Rosso wasn’t just betrayal — it was evolution.
It marked the point where Yuuki stepped out of the shadows and into the role of a genuine endgame player. By absorbing Greed and awakening Mammon, he positioned himself among the highest tiers of power in the series.
For fans searching for the real turning point of Yuuki’s character in That Time I Got Reincarnated as a Slime, this is it.
Not a battle.
Not a speech.
A single, calculated stab.
And honestly?
It’s one of the coldest moments in all of Tensura.
