Any minor chord can be interpreted as a second in a major tonality

There are three natural minor chords in a major tonality: second, third, and sixth. Any of these chords can be interpreted as the second. Obviously, the second, interpreted as the second, will keep you in the same tonality. But the third minor, interpreted as the second, will allow you to modulate into the major tonality one tone up from the current, and the sixth minor, interpreted as the second minor, will allow you to modulate into dominant major tonality.

So, with only the natural minors, using this technique, you can modulate to 2 tonalities.

You can also "minorize" the major chords – the tonic, the subdominant, and the dominant – and that will give you three more tonalities to modulate to: low ("napolitan") seventh major, low third major, and the major subdominant.

The total is 5 major tonalities that can be modulated directly from a major.

We can use the same technique to modulate from a minor tonality. There are three natural minor chords in a minor tonality: tonic, subdominant and dominant. The tonic, interpreted as the second in a major, allows us to modulate into the seventh natural major. The subdominant, interpreted as the minor second, allows us to modulate into the parallel major. Finally, the natural minor dominant, interpreted as the minor second, allows us to modulate into major subdominant.

Additionally, we can "minorize" the natural majors: the third, the sixth, and the seventh. This gives us the possible modulations to the low second "napolitan" major via minorized third, the low fifth (= high fourth, via "minorized" sixth), and into the sixth from the minorized natural seventh.

Additionally, we have at least two more possibilities with the "napolitan" major (low second major in both major and minor tonalities). In a major, we can take the low second major, "minorize" it, and then modulate to the seventh natural major. In a minor, we can take the low second, minorized it, and modulate into the high ("rised") seventh.

The easiest in all those cases is to use the sixth-chord.