I honestly do not remember writing this, but I still like it, so here it is. I believe I meant for it to take place in the manga canon, after Master Hawkeye's funeral but before Roy goes to war. It still makes sense if you haven't read the manga, though.
"Mr. Mustang..."
"Roy."
"Roy... I wanted to thank you."
"Hmm?"
"You've done so much for me, and I can't pay you back at all."
"Don't worry about it."
"No, no. I want to give you something."
"What?" He raised an eyebrow. This was unfamiliar territory.
"Please close your eyes." she said, in a very small voice. He did so.
He heard her breath coming closer and then... it stopped. For an agonizing few seconds, she stopped breathing. He was just about to open his eyes to see if she was all right when something very soft and warm ghosted across his lips, leaving behind naught but a faint feeling of relative chill and a slight, delicate wetness.
He kept his eyes shut, despite his instinct to snap them open and demand what had just happened.
"Riza?"
"Yes." her voice was nothing more than a murmur, as if she dreaded what was to come.
"May I open my eyes now?"
"Yes." she whispered.
He opened her eyes. Her face was flushed and her head bowed, preparing herself for the consequences.
"Did you kiss me?"
"Yes." even more quietly than before, keeping her eyes downwards.
He placed a finger under her chin and gently pushed her head upwards to face him.
"May I kiss you again?"
Her eyes moved upwards to meet his, before she said, so quietly it was little more than a breath, "Yes."