Complex numbers are just pairs (real and imaginary) of Cauchy sequences of pairs (numerator and denominator) of pairs (positive and negative) of nested versions of the empty set. (modulo al the necesary equivalence to make this work).
So the natural number {{}} is canonical included in the complex numbers as [something].
Natural {{}}
Integer ({{}},{})
Rational (({{}},{}),({{}},{}))
Real (({{}},{}),({{}},{})), (({{}},{}),({{}},{})), (({{}},{}),({{}},{})), ...
The definition taught to most mathematicians is that for the natural numbers,
In general But this is not how the real numbers are constructed. You either use Dedekind cuts, Cauchy sequences, or something else.