its funny that they were talking about forgetting and living a peaceful live. especially for this crippled girl, she must be an angel otherwise shes just as twisted as her.
It's more of forgetting a fear of her stalking them and turn that hardship into freedom from her, relief is what they now remember and makes them stronger.
It's like you bump your knee, it hurts, swelling and blood pressure cause irritation, but it got better now after a while, there might be some tissue damage but you're not hurt any more and it's all in the past.
If Ichinose would kill Midou, she would fully twist him and punishment for killing would be more severe, even though it should be treated as "self defense" there was still a clear murder with intentions.
Instead Midou staining his hands fully, he got punished a bit, but healed with a person that never really gave up on him being protected.