The introduction of Lieutenant Saavik is one of the biggest red herrings in movie history. We open with her voice entering a log in the Enterprise records as captain, then show her in Kirk's vaunted chair while the rest of the Trek crew—the familiar gang we all know from the series—go about their duties.
And we're baffled. Who is this woman? Why is she in command of the Enterprise? Where's Kirk?
But—gotcha!—it's all just a simulation, and Saavik is still undergoing training. When we meet her, we understand instinctively that she's not a part of the crew, her youthful ambition standing in marked contrast to the more weathered wisdom of her fellow officers.
And "ambition" is the best word to describe Saavik. She's bright-eyed and bushy-tailed, ready to get out there and show the galaxy what she's made of. We can see that in her obvious frustration at failing the Kobayashi Maru test. Like Kirk, she doesn't like to lose.
SAAVIK: I don't believe this was a fair test of my command abilities.
KIRK: And why not?
SAAVIK: Because...there was no way to win.
She's also is a bit of a stickler for military protocol, which we learn when the Reliant first appears onscreen.
SAAVIK: Sir, may I quote General Order Twelve, "On the approach of any vessel, when communications have not been established..."
SPOCK: Lieutenant, the Admiral is well aware of the regulations.
She might be little too brash and eager…but she's definitely right. In other words, she has the makings of a first-rate Starfleet officer. And as a younger character (and a Vulcan to boot), she makes the easiest and most direct representation of the entire crew of trainees: the people who Spock will mold and shape into heroes.
On a subtler note, she's also a good audience surrogate—especially for people who might not be super-familiar with the Star Trek canon. This lets her ask the questions that they people watching the film are asking…and even make observations about characters that the hard-core Trek fans know by heart.
SAAVIK: (in Vulcan) He's never what I expect, sir.
SPOCK: (in Vulcan) What surprises you, Lieutenant?
SAAVIK: He's so ...human.
SPOCK: (in Vulcan) Nobody's perfect, Saavik.
Her fresh observations, along with her dedication to excel and do her duty, helps Star Trek II pull off its greatest trick: looking at these characters with fresh eyes and showing how the old warriors of the original series pass the torch on to the next generation of officers.
Next generation…hmm. Now that's a good title.