Hey guys,
I don't want to be a buzzkill, but I just finished playing the game (more than once) with knowing the Japanese, and this game only pretends to be a "Simultion".
All events are the same and there is only one ending where you end up being with harem-like situation with both of your relatives, but literaly nothing you do in the game has any real effect.
The only difference is, that if you focus on a character, you can unlock more of sex scenes with the character, but you will still end up fucking both and always at the same date (you can't even affect that).
Ryouko (your kouhai) and Youko (your sister's friend) are just a tease and at least as I can tell, there are no sex scenes or any actual progress with them, which is a shame, because especially Youko looks really good and has interesting character.
And one last thing, the written dialog and what the voice actors say almost always don't match.
It seems the voice actors were allowed to change the dialog a bit to give their characters more of a personality, so what they are saying is actually way better than what is written in the box. Somebody forgot to fix it.
But that's all from me, I just can't help myself and wrote it here.