It happens in some manga, anime, and fanfic occasionally. Sometimes its done well, sometimes... not.
Take a couple, or a harem, and have one or more of their future children travel back in time to 'help' them in some way. Preferably, do it with a series that you haven't seen it done well in before, or in a way that you haven't seen.
Take a couple, or a harem, and have one or more of their future children travel back in time to 'help' them in some way. Preferably, do it with a series that you haven't seen it done well in before, or in a way that you haven't seen.