I get it. Mizuki once had the dream to become a mystery writer and she's into horror and thrillers. She knows Yuuki is well-connected and has contacts in the police and Yakuza so the best way she can do it is indirectly, bringing in her mom's kitchen knife and confessing to her friend's (or low-key Yuri crush) murder and trusting that the probono defense would suspect her cover story and want to investigate. The story has a lot of holes, and the exposition narrated by Mako, who's supposed to be dead could have been handled differently but I love the art so I'm still locked in