[Ginrai]

Originally Posted by Vallen Chaos Valiant

From the various internet blogs, about Sekai...

Spoiler for final episode:

It's said that Sekai wasn't pregnant after all, and that it was only a way to trap Makoto. Ironic, then, that this lie was the final straw that caused all the violence. Sekai didn't know that Makoto don't care to be a father, while the lie only enrages the other women to suspect foul play.

All in all, this is a tragic ending, but as it should be; Characters in the show brought this upon themselves.

Spoiler:

I'm not sure if it was a lie since her pregnancy wasn't that advanced.

If it was it's also possible by that point she believed in it, or she was willing to do anything to keep Makoto because he was all she had left (in which case Katsura's comment about Setsuna was likely more devastating than anything else).