Before the second Time Skip after Maria and Mamoru fled Saki had a dream about a faceless boy who said Maria had to die.
According to the Wikia this faceless boy was Shun
After his death, he appears in her dreams as a faceless person, as his name has been forgotten by her and the rest of Group 1
Considering that even if Missiah's apparent age on the wikia is out by 2-3 years there was no way Maria was already carring Mamoru's baby when Saki had that dream.
So why did Shun want Maria to die? She was one of his friends and also Saki's beloved. as a Karmic Demon could he also see the future and Missiah's birth?