What's the spoiler scene the happens different if you marry lucina?
Chapter 21 finale. Heavy Spoiler.
Right after Validar forces Robin to steal the Fire Emblem from Chrom, Lucina figures out it was Robin who killed her father, (hence the Premonition scene) and attempts to kill Robin over it. If you married her, you get this scene where Lucina ultimately winds up breaking down and thinking for herself for once and deciding that her husband's life matters more than the risk to her father/the entire world since you know, that whole Grima thing. It's more poignant since her entire character arc is centered on the idea that she matters, that she belongs, and she can put herself first. It's touched on in her Hot Spring Scramble conversation with Robin if they're married as well, where she says she can't put him first if it's her duty or him... then when faced with just that, she does.
Ah interesting... does this hint at them being the canon pairing? ---
NNID, PSN, and GT: Waluigi1 DD:DA Pawn: Xekoben the support mage