Also first part of side story
Spoiler!
The first part of the side stories are mostly about the birth of their child, Asiel who shows up even in the current timeline. Blair at first felt sad because even though the baby looks the same, he technically isn't him. Asiel appears to grow faster and act more mature than his age would suggest. Although he loved the maid, Ruth, and his mother, he would cry whenever the ML appeared. Blair feels guilty, thinking it was because of the negative emotions she felt towards the ML during the pregnancy. One night she talks to her baby, and said essentially that she is sorry and that she knows "Daddy loves Mommy," so he doesn't need to be terrified of him. After that Asiel stopped crying whenever he sees him.
Later, we learn that Asiel had his memories from the first TL, but because he was only two years old when the regression happened, he doesn't understand it himself. For example, hes protective of Ruth and tells the ML not to hurt him. For context...In the first TL, right after Blair dies, ML goes on a rampage while holding her body. He kills his own knights, Ruth (right in front of his child), and was just about to kill Asiel before regaining his sanity. This is where he regresses with some sort of magic circle he created(??) Asiel later followed them in the same circle. There was another situation with his birthday party and that's when Blair realizes her child is the same from the first TL. Also this man decides not to attend his son's 1st birthday apparently he can attend the future ones and it isn't a big deal 🙄🙄
I like to post spoilers for the stories I find interesting because I don't have much time to read novel due to busy schedule
you will find me in most romantic historical manhwa comment sections 
you will find me in most romantic historical manhwa comment sections