Note: I've used some personal theories as to Saïx's backstory in writing this. Also, if you have not played Kingdom Hearts 2, do not read this, since there are slight spoilers.
Chapter 2: Final Thoughts (Saïx)
My heart. I lost it so many years ago. I fought to the very end, but it was mattered not.
I wonder where my other half now is, whether it remains still within the Darkness, or if it has merged with the Moon in its glory?
The yawning emptiness is growing, spreading from my chest and consuming my flesh.
Is this what death feels like?
But still... I was bested by him, a mere child.
A child with a heart.
A heart...
"A heart... if I had a heart... Why... Kingdom Hearts... Where is my heart?"