So he needs to find a partner, be it love or lust something must be felt between them In Character. He'd probably prefer a Unicorn, but if the right mare comes along Equine and Pegasus could sway his hearts.
Reasons for this:
Relationships
Possibly love/hate
Babies
His Death
Now, his death idea may change over time. And the chosen mare won't have to do anything should you choose not to, but perhaps be at his side when he passes. (remember this is a long way out lol) But it'll give them time to interact and bond/fight with one another.
Side note: I do not have any foal passes, or even twin passes, though I'd like to have one. So if you have one that you're not using, or perhaps want to use with your character and Nato, let's do it!
Any takers? xD I'm honestly open to anything you might have an idea about too for plot reasons, be it shame for interspecies breeding or cheating etc.