Where the two water senshi are concerned:
Mizuno Ami is more directly the Senshi of Water in a broader sense, and her omnidisciplinary intellect is a mirror of the very universal aspects of H202. In particular she can wield mist as a cloak and is the one who can call upon and manipulate the power of the ice and snow.
Michiru is very specifically the ocean and her presence and her attacks carry with them the briny elements of the ocean and saltwater.
Ami’s power is less her destructive attacks and more her brain, as she’s essentially a one-woman industrial revolution in a box capable of inventing most of the magitek that the Lunar Kingdom in its various forms runs on, as is true of the people of Mercury in general (and Mercury, in this sense, is the foreshadowing of the Mars Mechanicum in the Phoenix Multiverse and a reference to it in other universes).
Michiru is the ‘doesn’t have a rogue’s gallery as her enemies are wiped out without a trace’ type.
