Red Stones Keep the Homunculi Functioning
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Dante supplies the shortcut
The Homunculi consume Red Stone material, tying their continued power to the same incomplete Philosopher's Stone technology the brothers encounter elsewhere.
Dante's access to that resource gives her leverage over beings who are extraordinarily difficult to kill but are not actually free from dependence.
Why it matters
Their apparent immortality hides another dependency. The Homunculi look like they escaped human limits, yet their existence still relies on somebody controlling access to the thing that sustains them.
Becoming Human Is the Perfect Promise Because Nobody Can Verify It
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The Philosopher's Stone as bait
Dante tells the Homunculi that a completed Philosopher's Stone can make them human. That promise gives beings born from failed resurrection a reason to help create the conditions for another Stone.
Whether Dante ever intends to deliver is almost beside the point. The promise keeps their desire aimed toward her machinery.
Why it matters
The Homunculi manipulate humans with false miracles while Dante manipulates the Homunculi with one of their own.
Lust Breaking Away Is More Dangerous Than Greed Running Away
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The question changes from freedom to identity
Greed openly rejects Dante and becomes an enemy. Lust's break is quieter and more threatening because she starts doubting the premise that made obedience worthwhile.
By the final arc she is willing to help Edward because becoming human has stopped meaning whatever Dante says it means.
What changed
The conspiracy begins losing control not because the Homunculi become weaker, but because they become more capable of choosing what they believe.