Why do Haruhito and that one woman look so similar to Makoto and Yukiko? It could just be "same face syndrome" from the mangaka, but in a chapter where it's revealed that at least 7 people look like Ai, it's weird that the last two people in the chapter look like Yukiko and Makoto, and of course, the woman who looks like Yukiko is shown naked...I'm really leaning more towards a "Mirai Nikki" concept here. Seems like all of these different people could be from different realities.
Maybe the small girl that was on the train who talked about mama and papa could've been Makoto and Ai's daughter from another reality, and the "dream" Makoto had after getting stabbed where Yukiko didn't exist could've been from another reality where he never met Yukiko. My theory for now is that, Yukiko is a yandere who likes Makoto, but of course, Makoto likes Ai. The "eye" in the sky could actually be the real Yukiko watching Ai, and "killing" her whenever Makoto confesses to her instead of Yukiko. The woman Haruhito sleeps with could be Yukiko as well, but of course, they don't have their memories. So, the real Yukiko could be trying to set up a situation/reality where she and Makoto can be together, but it never happens.