You've picked out some interesting questions, Crystal! And I think I'll do Shadow Man/Splash Woman for 27 and 35, and focus on some OCs for 33 (so these will be answered out of order).

27. What made you start shipping them?

I... honestly have no idea? Something about them just kind of worked to me, I suppose. Perhaps it has something to do with the concept that they present: man from outer space comes to Earth and falls in love and learns about life with a woman who is almost always in the sea. The land is merely a means to an end. It's value for one diminishes greatly without the other. Or perhaps it would be more accurate to say the opposite: that instead, having one another's company helps them further realize the planet's beauty.

That, and not finding any fics about them online gave me the incentive needed to start writing this pairing myself-

35. Is there a travel destination they wish to go to?

Yes! I think Splash would want to go to Paris quite a bit. She's heard good things about it, and wants to see if it lives up to it's reputation (and it being known as the "city of love" definitely adds to her curiosity). Meanwhile, Shadow would want to see the Grand Canyon. I think he'd be very intrigued by land masses or features that seem somewhat odd or out-of-place in some way. That, and he'd absolutely want to find a way for Splash to get there. Yes, his wife is basically a mermaid, but he will get her to that desert to see that rift in the Earth one way or another-

And now we move on to the last part of this ask:

33. Imagine this OTP on a couple date with another OTP of yours. How does it go?

Hm... I think the lucky couples we will be setting up for this are Demiastle/Woya and Palice/Persimmon.

I think the best way for this to work out is if we see it as Woya and Persimmon trying to force them to get along, since Demiastle and Palice are known to argue with each other quite a bit. Surely they'll play nice if they're in a public setting and have their respective significant others with them, right?

And believe it or not, it actually works for a while. The couples get to go to a nice restaurant, have some good food, and have a civil conversation. Everyone has a great time, and it seems like Woya and Persimmon's scheme might just have worked... Until on the way out, Palice makes an innocent statement about one of the dishes that Demiastle disagrees with. Somehow this escalates into them having a knock-down-drag-out in the middle of the parking lot. Woya keeps trying to mediate while Persimmon watches and keeps checking the time every few moments. After about 15 minutes, the two women give up and start shepherding their husbands back to their cars.