Inside.

You pull her tightly against you, you do not know if this fish, human hybrid beauty has a womb, or could even get pregnant from your human sperm but that is what you aim for as your mouth opens wide and you explode into her. One, two, three times your sweaty body jerks, shooting three large shots of cum deep into her. She is panting and raving in her unknown language, her pussy still tightly clamped around your cock, randomly tightening more, milking any sperm out of you it can.

She lays on top of you, your both panting. She starts to lay gentle kisses all over your body, her nipples still hard, poking into your chest with each deep breath you take. So she slides off, you set up to see her tail curved like the bottom of an s, to give her support to sit. Her fingers eagerly dig some of your cum out, to which she makes a gleeful smile, coos in her language, before burying the cum back in her and laying on her back so that it sinks deeper.

Maybe humans can knock up mythological creatures.