Oh my god, this. I refer to it this way: the sex is the icing on the cake. Too much and you ruin it, not enough and it's dry. It's a very fine line.
It's pretty similar to how I describe it. The same way but with salt or ketchup. Too little and the is bland and tasteless, too much and it is inedible.
Going back on track. Definitely a story with a non-human female. I want something different, something that would have an effect in the dynamic of the rp.
How would the non-human character has certain advantages over mine and how can she use those in the story and how my character is more suitable for other situations? How both make up a team better than the sum of its parts.
How do these difference impact the bond? What draws them close despite their differences? Is it easier for them to have something or do these differences make more harm than good?
What are the good sides and bad sides of being different? Maybe the non-human can't give hugs without slicing her partner in half. How would that affect her mind? What solution can the characters come up with? Are there any advantages for the relationship? Maybe the non-human is smaller and can be snuck to places she shouldn't be, maybe she is big and allows for extra comfort.
And why not? How do these differences come into play in the intimacy? How does it feel? Does it have any side effect?
In my Pilot x Ship scenario intimacy (sex) is not only a physical connection, but also a mental one. Slow lovemaking can mentally feel like lying on a warm pool and floating carelessly. Fast and passionate sex feels like they are performing acrobatic flight or riding a rollercoaster.
Sew everything together and it can be something quite enjoyable to write