The analogous word would seem to be "duality", but one would need to see the full context to be sure that it fits.
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Laohg ReaperIt is two person in one ***.Yes, it could work. For example, this is an example randomly thrown up by Google search which reads fine:
Laohg ReaperWhat is 'two deities in one' called, if 'three deities in one' is called a triune deity?Apparently the word is "biune". This is a very rare word, and I think most native speakers would not know it (I didn't). However, there are a few credible-looking Google hits for "biune deity", so it seems that the term does actually exist.