Thank you for telling me about the Zero/CC dialogue mistake. I didn't notice it before. I have now fixed and patched the game.
If you are interested in "Nulls" and the "Upcoming war" then I would recommend " "A Happiness Story" and "Goodbye Time Traveler". The former actually takes place after the events of this game and the latter is mainly what triggered the "War" in the first place.
As for CC, she is present in "Goodbye Time traveler" and in her short spinoff game "CC: the girl who chants love at the edge of time". She is also present in other games in the series but it's more like cameos.