The thing with Kokoro is so damn frustrating to me because the beautiful dramatic irony was so close I could taste it! Having her leave Futoshi for Mitsuru, only for Mitsuru to leave her for what's basically the same reason she left Futoshi, but no one involved is really in the wrong would have been great. It might not have been what some people wanted to see, but it would have really made the show a lot more interesting.
A part of me can't help but imagine they had interesting plans early on, but then a bunch of Japanese SWAT burst in and announced this anime's production had been nationalized on order of the Prime Minister.
Really, this isn't just jumping the shark or dropping the ball. This is launching your into space on a Saturn V while firing a Ball out of a railgun into the center of earth while the guy from the history channel with the weird hair says aliens are responsible. This show had so much potential in terms of themes, and after episode 15 it seems like they decided they wanted go the most stale, boring, inoffensive route possible.