You glance at Fawkes, who must have followed you here after sensing you're in danger, who showed such loyalty to you, you think of Dumbledore, your friends, Ginny. Your parents.
You feel an enormous power in your soul.
You hope this works.
Most importantly, you have hope,
A bright yellow smokey charm hits the basilisk square in the heart, enveloping it's whole body in a bright yellow glow. The basilisk stops short and shifts uncomfortably.
Silence falls, the most intense silence you have ever experienced. And then... then the basilisk shrinks into the size of a grass snake. It hisses silently and slithers quickly, disappearing in one of the Chamber's crevices.
Oh wow, it actually worked!
You gawk at the spot the basilisk was looming just a second ago, not believing your luck, until you hear a cold laugh from where Ginny's body lays.
'Well then, I seem to have underestimated you. Most annoying, but fear not, once I gained my powers back fully, and once this girl's body gives in, which wont be long now, then I'll...' your attention trails of as you feel s little peck at your back. You look behind you where Fawkes pushes a ..fang? towards your leg. You pick it up and do the only thing you can think with it - pierce the Tom Riddle's diary that's laying near Ginny.
Voldemort releases an angry scream but fades out of the view before he can say anything else.
Ginny wakes, and before you explain all of it to her, you make sure to thank the Phoenix.