DAMMIT.
Her story brought about the best developments. Isaac is going to get boring without her influence, and Mine could've used the confidence from being able to help her.
Not that I'm not also depressed that a small child who spent her life abused and finally had things looking up got tricked into jumping off a bridge by the same kid that drew Kujou's attention to her in the first place. This just happens to fall under 'unnecessarily tragic.'