The ending. Just... the ending. If watching Kyousuke save Haru's future and career by lying bold-faced about how much he hates Haru and tried to pin the crime on her before confessing does not get you, the investigator asking him to just admit that he's lying because he loves her will.
This is all made worse when each of the other love interests in turn appears for a heartbreaking scene where Kyousuke must act coldly towards them and send them away to maintain his facade. If you've already got to know them on each of their routes it will be a Trauma Conga Line for both you and Kyousuke.
And if that doesn't get you, then there's the fact that Haru waited for him for eight years, rather than marrying Iwai, will. This is to the point that she is there the moment he is released from prison, along with the daughter she had by Kyousuke.If you are not crying through the Interrogation, the end will tear you to shreds.