I take it you chose the sacrifice ending?
While that is the best ending (I mean, for Lucina x Robin it lets Robin keep the promise he makes during their romance conversation in the Hot Spring Scramble DLC: to support her for the rest of his life, even if he has to find a way to come back from the dead to do it), the other ending does have one nice thing about it that the sacrifice ending doesn't have: unique dialogue with Robin's love interest.
Basically in that ending you have Robin feeling guilty for not sacrificing himself to stop Grima for good, with Chrom, Robin's love interest, and kid(s) all assuring him he did the right thing (with these lines being different for each character)