bruh
No I'm pretty sure it'll go with Erika and also he doesn't even think of Sachie as a woman at all. Though because Erika told him to, he did end up having to be conscious of her.
I think Erika is way too nice to her even though Sachi is being rude. Like, Erika and Nagi just got engaged and they just started living together. The whole purpose of living together was so that they could be more conscious of each other and getting along together. It's incredibly rude to barge in on a new defacto couple and start freeloading. Sachi also throws lots of fits and thinks it's fine. Sachi needs to realise that even though she is Erika's sister, she just met her. Like you said Erika is super nice to her just cos she knows she's her sister now. But Erika also gets hurt like how she got hurt this chapter cos Nagi turned Erika down for a shopping date and then he went out with Hiro (I think it was)
NOOO EWWW PLEASE DON’T TELL THIS STORY IS GOING WHERE I THINK IT’S GOING WITH THE WIERD INCEST LOVE LINE EWWWW (yes i know they’re not actually brother and sister but still