What makes you think she'll have a bad ending in his route? Just because he could be a yandere (as per what another poster said above about the deres that haven't been used yet) doesn't necessarily mean she will have a bad ending.
A yandere?
Yikes....
I was worried caused Katarina was the one who unlock the secret route caused she kinda make all four (plus the girls) to like her. What if she fails making him fall in love too? Or even worse, he likes the real heroine so there is a chance she will get bad ending.
Doki doki literature clubs makes one paranoid about endings.......
Why did you have to bring up Doki Doki literature club. Now I'm paranoid too.
LOL (≧∀≦)
The mc, Katarina has managed to avoid all the bad endings but she hasn't avoided the bad ending for secret route yet!!!!!!
Oh no!!!!
Run!!!!!!!