Diabolik lovers has been weirdly good for my mental health. It's gotten me to fix many of my harmful or self destructive tendencies, because the characters basically cover the full range of unhealthy and shitty behaviors a person can have, so if I'm acting anything like a dialovers character, I need to check myself.
I stopped self isolating and trying to make people mad at me when I was having morality spirals because that's Subaru behavior.
I stopped assuming that people hated me because they did things that I never actually told them not to because that's Kanato behavior.
I'm trying to stop ignoring my limits and holding myself to the standards of a healthy person (I'm chronically ill) because that's Carla behavior.
These things still take work, it's not a perfect system, but it's really helpful. Diabolik lovers has genuinely made me a better and more stable person.
Of course, this means I had to tell my therapist about dialovers, and now she asks for updates about what's happening in my fanfic every week.