Well, simply play the game, read hints near characters icons(Left side of screen on PC/Swipe to the right on mobile)If none of this helped, tell me what stage of the game you are currently at and I'll tell you what you have to do.
I'm at the eND of sakuya's story then I updated to 0.7.9. (is 0.7.9 just a bug fixed update?)
Ah, well yeah, if you already seen Sakuya's content, then that's it for now.
ohh I see, thank you