Haha, after a few translations, our communication has become a bit difficult.
1- I infer that monogamy still exists in the future based on what Cathy's brother said at the end and what the protagonist thinks. I feel that it’s quite normal for the protagonist to think this way, but it’s not so normal for people in the future. As for not seeing the meaning of love, I believe this is the difference between the protagonist and others; he understands how to love better than people from the future. I actually didn’t see that plan because I helped Cathy. The infertility issue is actually my argument against the existence of monogamy in the future.
2- I think the protagonist having a harem is more in line with the apocalyptic background of the game, haha. Author, is it because you don’t like harems that you didn’t include one in the plan? I understand that Chloe won’t enter the harem, but Cathy and Octavia should be part of it. Perhaps our definition of harem is a bit different; do you think a harem is when all characters are with the protagonist? I believe a harem consists of a few characters, like those female characters from the future, Cathy and Octavia.
3- Due to translation issues, I didn’t quite understand what you said about Octavia. But I am glad to know she is original.
4- As for the protagonist's ex-girlfriend, I actually don’t like her; haha, it feels like she abandoned the protagonist.