Both pairings involve a woman who is born into royalty and a man who is a common-born criminal o outlaw.
Both couples involve a hero and a redeemed villain. Both villains were seeking revenge for the death of a anterior love.
Both couples are segundo chances at amor for all characters involved. Emma's first amor was Neal Cassidy while Killian previously loved Milah. Regina previously loved Daniel while Robin was married to Marian.
Before Regina let Daniel go in The Doctor, he asked her to amor again. Before Neal died, he asked Emma to find Tallahassee - their hoped location for a happy future...