Really peak chapter here, we got two problem child sisters in one (even though Toudou isn't quite sure of that), Yanagi had her sister issues manifested, and required some classic Toudou speech to bail her out, and the gang together for motivation.
One potential I think could work is that Yanagi could actually bond with Toudou by their ... not exactly bad relationship, but troubled relationships with their own sisters, because they care about each other, but it's shown in kind of a twisted way, that makes them miserable in a certain way. Still, there may be some issues when Yanagi joins the polycule and has to face Rin and Kurohime's judgements for being there first (plus Rin's personal animosity towards her, since she claimed that if it was Yanagi instead of Kurohime she would have no issue beating her to a pulp) but it would probably take a few months or maybe a year to get there, so we'll cross that bridge when we get there.
Oh, and the author really did that dirty with Kouno opening her mouth here, and indulging the author by making them wear swimsuits all the time...hehe...
Thanks for the translation! Mochi Author Lait sure is cooking real well!