'God killing plan'
I'd say the idea is to become the most powerful mortal in the world. Take out others with Geass*, expand his Empire, that sort of thing. Probably wants to take out the immortals too. We'll have to see what his pact with V.V. was before we know for sure though. Or we can just hear the plan, either way should give you the answer with enough thought.
*note, that doesn't necessarily mean 'kill'
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