If you go back to the 1088 case that preceded this one you'll see how the director back then, Kabumoto, got the nickname of the Marionette Devil. He doesn't just drill lines into his actors, but he controlled their lives outside of the stage too including encouraging murder, affairs and probably all manner of shit and made it clear that he approved if it gave a better performance.
Kuraishi has admitted that she was in the previous production and in teaching her the Kyoto accent it's likely Kabumoto was taking a special interest in her and grooming her in a similar way to the perpetrator of his own murder was. That isn't the same as proof, but I am guessing it will be a factor, because it is the shadow of Kabumoto and how he manipulated people that is the focus of what's happening. It's not just the 2 actresses posed like marionettes, but the current director getting hit by a car too. I think it won't be Kuraishi who is the murderer, but bad treatment of her that forms the motive.
Look back at what happened on page 13 of the previous chapter, especially the bottom 2 panels on the page. If Tenma loves his school friend and is maybe a bit unhinged (as people often are in DC) then Narasawa signed her own death certificate right there. It usually isn't the most obvious suspect, bearing in mind everyone else was in the same room so, unless a trick was somehow used everyone else apart from the next victim was alibied, up, but maybe this time it is, so that a large part of the chapter can be taken up with Hattori confessing his love. Nothing is a greater aphrodisiac than a confession of love high up in the sky by a big window after you've just seen 2 people falling to death, right guys?