Why is she bleeding? In that world, women apparently are far more repressed sexually by society and by individuals of the opposite sex. So it`s safe to assume the girls are more that accustomed to penetration, moreso if the have 16+ years old like the big sis.
... Did you miss the fact that in this world, the human sex ratio is so heavily skewed in "favor" of females (1:39) that most girls and women have never interacted directly with a male, much less engage in romantic or even sexual activity with them?
And before you say "dildos", the fact that none of the horny girls in the main story even remotely allude to sex toys implies that they either don't exist outright for some reason, or the women simply don't develop a libido until they come into contact with a relatively attractive male and he doesn't act like an asshole (which is shown to have a sufficient repelling effect to prevent horny reactions), and thus there's insufficient economic demand for a sufficient supply to be produced that would make the prices affordable for the average middle-class consumer, i.e. sex toys are largely the province of rich people, and that's complicated by the fact that great wealth makes it that much easier to secure male "company" anyway (i.e. even less demand).
