The 100 Girlfriends Who Really, Really, Really, Really, Really Love You - chapter 219
The 100 Girlfriends Who Really, Really, Really, Really, Really Love You - chapter 219

danke.moe
The 100 Girlfriends Who Really, Really, Really, Really, Really Love You | Chapter 219 | Danke fürs Lesen

About time someone acknowledges that these characters straight-up have superpowers.
Nakamura (the writer) has been cooking, doing plenty of set-up for a future Yamato household arc.
The obvious approach is for Rentarou to zing with Miss Naddy's younger sister and rescue her from the abusive family. However, knowing Nakamura, it will probably be something badshit again.
I hadn't really considered it, but you're right. There's no reason Naddy's mom would be off the table other than maybe having too much overlap with Yaku. I'm still guessing it'll be her sister though, and that the aforementioned sister was also the ninja we saw at the end.