I don't get it

Ever see that movie Sliding Doors? About a what if story if x did or did not happen?

This is basically like that. Two stories, one in which Eren is the one hurt and one in which Levi is. The one hurt dreams they are the one not hurt? Or it's not a dream and we cross over the other side of the what if.

I don't know. But in each one it's a love story but depending on the character who is hurt it changes from requited to unrequited due to misunderstandings. I think.