To be fair what kazusa mean by 'everything lead to es II cross' that once you truly love someone you'll get into the point of acceptance, this include accepting his/her flaws AND their naked body. This don't make these girls perverted by thinking about es II cross. Most men think sex as their tool to release their lust/desires, while the women thinks sex as an acceptance that the guy actually want her and that they're worthy, because most women is very insecure with their body n appearance. Hence why girls do this kind of things like dressing, make ups, etc, not only to attract men, but also to make them feel good about themselves, to not looked down, ignored, or underestimated. This was perfectly visualize too in the 'rain of cute' scene with sonezaki senpai. Just want to point things out Unless it was obvious don't @ at me.
Tl:dr
Girls thinks es II cross as a form of acceptance (love&lust) because they're insecure (most of the time) with what men thinks n want.
Also Okada Pls don't make this one generic HS romance I beg u :'