Who do you think is Ren's mother: Hashi or Reira?

We already know that Ren's father is Takumi. So who is the mother?
I suppose there is a good reason for Ren live in London and like Reira so much, playing to her and everything.
Or do you have a completely different wild theory?

Little Ren looks alot like Reira. I'm guessing that Nana decided to care for the child as if it were her own. Perhaps Reira is not ready to be a mother and still wants to maintain her musical career.

I think it was in either volume 20 or 21 where Takumi and Nana are separated because Takumi is so career oriented and I think eventually Nana became aware of Takumi's affair with Reira. Nana's good friend, Junko, was suggesting to Nana about divorcing Takumi yet Nana was adamant that she wants to work things out with Takumi. I have a gutsy feeling that Nana may end up with Nobu after all.....or maybe not.

I must confess I will be greatly disappointed if Nana ends with Nobuo. I don't like how he acted when he discovered her pregnancy. He had no courage to tell Nana that he would stay with her and her child - as Takumi did. Takumi won me because of that. At first I thought he was just a selfish bastard but after all he did for Nana and a child that he wasn't sure if was his I had to give him a lot of credit.
But is very possible that Nana give up on him because she is capable of the most stupid decisions.
I wonder if Ren is Reira's son. I'm still not sure about. I remember chapter 20 and that conversation. I hope Nana and Takumi makes the things works. I believe he really loves and need her.

I'm with you daniyagami! and by the way I'm new here, for me Nana is the best josei anime, it is so close to real everyday life, and i think Ren is Nana's 2nd child, I'm not sure in what chapter says or suggest that Nana and Takumi have 2 kids, as for why Ren is with Reira I think is because he took a like of Reira and since Reira didn't stop feeling guilty about the accident!! sorry if I'm wrong about all this , and I know for sure that Takumi really loves Nana, he's just to damn workaholic and the too flirty part (yes he's is very flirty) is all for the career image thing.

Well, it's late to be joining such a discussion, but I think Hachi is Ren's mom. Ren seems older to me than Satsuki, so maybe he's actually Hachi and Nobu's? He could look like Nobu. At least that's what I think...and why Takumi might have wanted another child. He does seem to dote on Satsuki. I want Takumi and Hachi to stay together! The fact that he's working toward finding Nana and thinking of Hachi while looking says to me that he still loves Hachi and wants to try. At least I hope so!