I’m still confused how the hero freed herself and and started killing him for no reason.
The skill "Save & Reset" is something that the Hero gave to MC. Which is why she isn't completely affected by the reset unlike others, and her soul ends up carrying some partial memories of each reset.
This had enabled her to carry some of her feelings from her previous round before she committed suicide.
And apparently there is another personality inside the Hero which is using these partial memories to target MC and any girl who tries to get near him.
Lastly, the Hero didn't really free herself from the seal, she is still stuck inside.
It's the another personality inside her which is somehow able to manifest herself outside the seal temporarily which is going around killing MC and any girl who gets near him.
Which is why she always suddenly appears, as she is manifesting herself on the spot.