Fridge Horror/Anime and Manga/Naisho no Tsubomi

Fridge Horror

In Naisho No Tsubomi it turns out that Saya really is Tsubomi's unborn sister who came to the past to tell Tsubomi she loves her (and give her and her friends some sex ed for whatever reason). But why did she felt the necessity to go back in time to tell her that, if she would have plenty of possibilities to do so in the future. Unless, of course, something terrible would happen to either Saya or Tsubomi...