At first glance, the song seems to be a “neutral” LTD song: one that could just as easily apply to Cloti. But the singer calls the girl a “light” and as someone who “changed” and “saved” him, which I think speaks more about Aerith than Tifa. Cloud sure is more ‘changed’ and lighthearted with Aerith, and she’s a natural at ‘saving’ him from moping and depression.
And of course, the repeated phrase “for you” reminds me of Cloud’s famous Clerisy quote “But I’m—we’re here for you, right?” :)
I think it captures best Cloud’s protectiveness for Aerith before she died.

For You
The Calling

I am a vision
I am justice
Never thought that I could love
Living in shadows
Fading existence
It was never good enough
Within the darkness
You are the light that shines the way
But you're trapped in violence
I can be the man who saves the day

Chorus
I'm there for you
No matter what
I'm there for you
Never giving up
I'm there for you
For You

Someone's changed me
Something's saved me
And this is who I am
Although I was blinded
My heart let me find out
That truth makes a better man
I didn't notice
That you were right in front of me
Our masks of silence
We'll put away so we can see

(Chorus)

Within the darkness
You are the light that shines a way
In this blind justice
I can be that man who saves the day

I'm there for you
No matter what
I'm there for you
Never giving up
cause you know it's true
You were there for me
And I'm there For you
For you
For you