@DrPavel this really isn't all that alarming when in my everyday life I have my mother inches from my face for a kiss on the cheek or for a hug or something along those lines. I think the intentions of the author is to reveal who the mother really is beyond the chapter prior to this one. We've been learning bits and pieces of what his mother does and what her personality "might" be like but now we see that this is what she's really like. The way I see it is like this, when you're growing up you always see your parents in a certain light but when you get older and interact with one another there's a side to them you never knew about and here we're seeing that Rei is now aware of something he didn't think his mother was capable of.
@starlightcitypro I don't disagree with your first point it's just the way she did it in the beginning it was very subtle way like saying, "I'd die if you weren't here." but it'd come off more as a joke than a threat. Here she's being coercive in a way that's akin to a villain revealing their true colors where it's quite clear that they're up to something but not quite clear on the specifics. Before it was just that she's in a tough spot and manipulates him to do things for her because her hands are full.
The majority of the cast are not good people including ones we don't see like his father. I'm still reserved on the mother because she's in a situation where her environment shaped her into this and I don't know what her motivations are. If she didn't have her other son and mother to take care of I'm sure she'd let Rei go do what he wants but she can't afford to let that happen.