Ok, so I think im getting an idea as to what happened. So hear me out. The wife has postpartum and maybe she thought that our girlie was taking Keisuke away bc that was her only line of support with her husband being MIA due to work. Without Keisuke, she'd have no one to help or support her. She'd be alone. So, she confronts girlie with a knife on the roof. Its dark, hard to see. Just as she's threatening her and rushing toward her with the knife, Hiroki steps in and grabs the knife which is why his palm has that deep ass cut scar. As he's trying to take the knife, he accidentally backs into our girlie and she falls over the roof. But, he can't deal with her right away. He's dealing with his wife who probably just had another mental break over her realization of what just happened and what she did. So, im thinking Hiroki dealt with his wife first while calling the ambulance for our girlie. Wife isn't there at the scene of the crime bc Hiroki moved her. The ambulance arrived and he left with the knife. He wiped it down and tossed it bc he didn't want his wife to go to jail, clearly. And the blood that was found on the knife to be AB is his