well in her case it wasn't consensual. Her virginity was literally taken by magical dick worms.
I'm not a virgin
Oliver Turner
Robert Williams
Tsukhime is truly a story about optimism, valuing yourself, appreciating your life, and moving boldly into the future. Death might not be as close to our doors as it is to Shiki’s… but, then again, you never know. That is why the lessons in this story are so applicable. You are alive now, but maybe not tomorrow. So look on your past fondly, smile at yourself in the mirror now and again, and hope lovingly for the future. Shiki is someone who has about a decade or two of life left, and he messes around with two immortal beings in the main routes.
In the epilogue, Shiki fatefully meets Aoko again and they muse a little bit about old times past. Shiki notes how the past several days/weeks (the span of X route) have been crazy. And some point Aoko tells him that those days will eventually end. Shiki agrees and asks something to the effect of when. The Magus just kind of remains silent and freaking Shiki just tells her that the days were fun, though.
And this is what, for me, Tsukihime was about. Yes, there were vampires and serial killers. But it was really about finding joys in today – even when it doesn’t seem like there are any… and about having faith in a tomorrow. Basically, Tohno Shiki could die ten years from that conversation with Aoko, or he might not even wake up the next day. Although we don’t “live close to death”, the same basic concept applies. There are no promises in life. So you can go through life miserable only to be potentially snuffed out tomorrow, or you can find your own happiness and hope it extends into your future.