Here's a list of couples or pairs of characters I would love to write about, but don't have the canejos (yes, rabbits) to do it:

Hohenheim x Al
Al and Martel
Armstrong x Rose (Come on, people! The movie!)
Scar x Rose
Al x Winry
Ed x Martel
(Anime) Pride x Sloth
(Manga) Wrath x Riza (non-con)

I'm sure there are more and I will probably be spamming folks by editing this post off and on.

Thank you and good day.