The story tells that
human Lemiel's sister and Licht conceives a child together, hoping that it will unite humans and elfs. Immediately following the wedding of Licht and Tetia, a group of human royals attacks the elves and steals their magic for themselves Licht
What happened with the baby of Lemiel's sister and Licht?
The baby dies before it was born because Lemiel's Sister died.
When all the elves take over humans, the baby takes over Yuno. This is why he was able to break out of the Paotlli's command because the baby's brain was not developed.
This is further evidenced in the manga in chapter 213 when Litch tells Yuno that he was able to fight beside his son who was inside Yuno.
