I think it would have been better if Marina stayed in the past, like if Rinosuke's future self was dead rather than just in a medial coma. The whole plot and concept would have been the same, they just would have gone with the multiverse theory instead of the past changes the future theory. It would have worked out better for their relationship to, where Marina came to love the current Rino rather than the one she attempted to make him become. Having her leave him like that kind of felt like the development of her and Rino's relationship was almost for nothing if she just went back to the future him, especially since she fell in love with the past Rino. Not only would doing this have been better, but they also could have made the manga a volume or two longer. Having changed the past from what Marina knew (i.e. Rino's marriage to Masaki, the loss of his friends, etc), they could have done something where they wondered what these changes would mean for Marina's past self, and done a few volumes on that, like that past Maina was never born, or her parents had a boy instead, making Rino and Marina wonder what would become of her or their future. In any case, I think it would have been better if Marina stayed in the past.
I think it would have been better if Marina stayed in the past, like if Rinosuke's future self was dead rather than just in a medial coma. The whole plot and concept would have been the same, they just would have gone with the multiverse theory instead of the past changes the future theory. It would have worked out better for their relationship to, where Marina came to love the current Rino rather than the one she attempted to make him become. Having her leave him like that kind of felt like the development of her and Rino's relationship was almost for nothing if she just went back to the future him, especially since she fell in love with the past Rino.
Not only would doing this have been better, but they also could have made the manga a volume or two longer. Having changed the past from what Marina knew (i.e. Rino's marriage to Masaki, the loss of his friends, etc), they could have done something where they wondered what these changes would mean for Marina's past self, and done a few volumes on that, like that past Maina was never born, or her parents had a boy instead, making Rino and Marina wonder what would become of her or their future.
In any case, I think it would have been better if Marina stayed in the past.