Hi, everybody!
Guys, this is just a prologue, and the game is not about NTR! Sister, mother, niece, and Yumiko love or will love only MC! But, for example, the sister has reasons why she distanced herself, and it's not Nate, but their parents (and the fact that parents will not accept such a relationship)! And there is such a dialogue in the game! They both understand that they cannot be together and make an informed choice! Once again, the reason is the parents! I don't understand why you perceive that Nate took her away!? This is due only to school age...
In the future, everything will be good! Sister, mom, niece, and Yumiko will be just for MC!