Plus, plotwise, it makes sense with the whole "change the future" thing. Haven't played Future of Despair yet (or whatever it's called, I know something is called that) so not sure how Morgan would work there with this pairing. I keep starting over to try and optimize pairings to my liking and end up getting bored/wanting new combinations before I finish, so I haven't gotten around to those maps or Apotheosis yet.
So far, as far as Avatar goes, I've done Robin x Lucina (first run), Robin x Chrom (second run), don't recall my third run, and currently on my fourth run with a preliminary aim of Robin x Lissa (since I want Owain with Armsthrift, and don't like the only two options that grant that outside of Robin).