In her mouth, but tell her not to swallow just yet

You drag your cock out of Tifa's mouth, and she gives a wordless, agonized cry, as if starving for more. "Now listen," You say in a hoarse voice, gritting your teeth and holding back your orgasm. "I'm going to cum in your mouth, and you're going to keep it in there. Don't swallow 'til I say so!" Tifa opens her mouth, sticking her tongue out so that when you jam your cock back into her mouth, she can lick your balls while you ram against the back of her throat.

In seconds, you feel yourself cumming, and you pull back just in time to leave just your dickhead in her mouth. She moans as your cum fills her mouth, and when you pull out of her mouth, she closes her lips so that she doesn't spill a single drop.