This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Robotics;Notes
The end of episode 16. After nearly unlocking the next Kmijima Report, both Kai and Mizuki get a strange call that plays an odd sound file. After that, Mizuki's robotic exoskeleton begins moving towards the edge of the cliff they're on. It takes Kai a moment to realize what's going on. When he does, he immediately tries to stop her, but the legs are too strong. Kai even manages to knock her over, but the legs push her back up again. When it seems like Kai is going to go over the edge with her, she knocks him aside, and Kai can only helplessly watch as she goes over the edge of the cliff. Oh, and while all of this is happening, the Gunvarel Mark II seems to have fallen onto Subaru.