
I agree that Tsumugi is at fault for thinking it would be fine and not doing anything. However, I do think they need to talk regardless. Itoshi is falling to pieces and pretending to be fine. While the baby isn't going away there are things that can be done like Itoshi going to therapy or parenting classes because his main issues appear to be that he doesn't want to be like his own parents.

No it was an accident. Equally their fault. And you can’t just run to the store to get a Plan b in Japan. You have to be prescribed it and pay a good amount of money. Really knowing his hold up about the idea of a child he should have asked her to go to an appointment and then paid for the medication well ahead of time for accidents like this since emergency contraceptives are best taken within 24 hrs of intercourse. They both are train wrecks tho ngl. And it ain’t been fun for a while but I gotta see it thru.
This is going to be an unpopular opinion and I'm probably going to disagree with myself in the morning but... It is kind of Tsumugi's fault right??
They have discussed children beforehand and Itoshi made it 100% clear, that he does not want children. They then had sex, where Itoshi wrapped his willy, but it slipped out.
Contraceptives are hard to get in Japan, yes, but "Teehee, all my ex-boyfriends did me raw all the time and I didn't get pregnant yet!" is a really immature response from Tsumugi, when she knows, that Itoshi would hate raising it.
She then finds out she is 100% pregnant and decides to keep the child. Note, that I do not consider this as "part of her fault" as keeping the child or not is entirely her business. But!!! She knows, again 100%, that Itoshi does not want to raise the child and when she sees that he's trying to be strong for her, she tries to talk it out with him.
Here is where I'm completely on Itoshi's side: what is there to talk out?? This isn't a topic where the right string of motivational words will change anything. He doesn't want a child, but the child isn't going away. Unless Tsumugi was going to suggest abortion or splitting up, there is nothing to discuss. Making him talk about it, when it's obvious even to her, how much he doesn't want the child, yet is staying strong for her, was not at all malicious, but it is hurtful. Obviously don't yell at your pregnant girlfriend, but since he met her family, he has not had it easy ughhh.
This is such a good manga aaaaaagghhhhhhh. So much nuance, so much personality, I love it. I will implode if we don't get a someone-listens-to-Itoshi chapter soon though (note: listen not as in "I can hear you out", but as in "We can do something about this"), bro literally doesn't trust anyone, but Tsumugi and now he has to face his worst nightmare to be with her ahhh.