Who is the father of the boy?

I liked this movie.

One doubt: Akiyo is pregnant, but who is supposed to be the father of the boy? The violent customer or the friend Kikuchi? As I understood it, Akiyo went to the gynecologist because of vaginal damage, but did she got the news (or guessed that) she was pregnant then? Or rather she got the idea to conceive a child, and then went to bed with her friend? Or perhaps, knowing that she had a good chance to be pregnant from the customer, she planned to get unprotected sex with her friend so that, in the event she had a child, she could think that it was (perhaps) from her friend? What do you think?