"see someone's true nature" is correct and natural. However, your sentence is unclear about who is drinking the alcohol.
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AnonymousThe person whose true nature you see is doing the drinking. Should I change the sentence?It may be that the rest of the context makes it clear. If not, you can either leave it alone and hope that most people will interpret it the way you want, or you could say something like "Alcohol can cause people to reveal their true nature" or "When they ar