I must have missed something... it seems that there are supposed to be multiple routes, but when I played through, I did not see any choices to change anything, and I finished on an ending with Asahi.
At that point, all of Asahi's gallery is complete. The rest of the girls' galleries are empty except for the first picture in each one.
Sometimes there appeared at the top of the screen a frame with the four girls' profile pictures but it disappears almost immediately, and I was not able to experiment with it.
EDIT:
I found a post with download link to a walkthrough, but I don't understand how to use it.
I get that kissing or not kissing a sister has something to do with it (on my playthrough I kissed everybody every time), but the references to white dots and black dots and " * " are not clear to me, and I don't understand all of the Kiss, Kissing, and all that stuff with white or black dots and names or "good" or "pod" or "yes" or numbers 1, 2, or 3... I am very confused!
Maybe if someone can explain the first few sections under "Common 1", I might make heads or tails from it:
It starts with this group:
○ Kiss (Asahi)
○ Kiss (Mahiru)
○ * Kiss yayoi (yayoi)
○ Kiss (Saya)
I am guessing that means to Kiss each sister, but what does the asterisk before "Kiss yayoi (yayoi)" mean?
And is there a reason for yayoi to be repeated (Kiss yayoi (yayoi)?
The next group:
○ Kiss (Asahi)
○ Kiss (Mahiru)
○ Kiss (yes)
○ Kiss (Saya)
what does "Kiss (yes)" mean? Is that supposed to say "Kiss (Yayoi)"?
In the third group, why is each kiss line repeated? What does "Kiss" (without a name) mean? (same as "Kiss (yes)"?)?
If someone can explain these to me, maybe I can make some sense of it.
Also, the link to the Saya third person speech quirk seems to be broken. Where can I download it?