Damn, i already knew the summary but reading through what their conversation was, makes me wanna use a neuralyzer on myself. From being always in control to not being able to control her own lust, oh how far has she fallen. Yuichi should have just learned how to do S/M stuff since Hinako is clearly a masochist, satisfying her through toys would have been enough instead of gambling with diseases and pregnancy from another guy being involved and given the fact that it will always go back to Gouda once she can't handle it anymore since clearly he imprinted on the sisters.
In an alternate universe Hinako caught Yuichi looking at S/M stuff while imagining what he would do to her instead of getting off the idea of being cuckolded. Then they indulge in both public/private S/M acts that could break destroy their reputation and made a hidden account where they do live S/M stuff with Gouda just making Yuichi watch the video of a S/M channel not knowing it was Yuichi and Hinako in the video.... Damn i should read Nana to Kaoru again.... but holy sheet i don't like AI but having Hinako getting tied up with all those juicy expressions would be a sight for sore eyes.