Hookman mystery

As usual, Suou arrived at the building to try to speak with Mayuri. She managed to find her again, though they only spoke through the walls without actually seeing each other (even though there was a CG showing Mayuri's full body). Mayuri insistently repeated that Suou shouldn't be there. When Mayuri's voice eventually faded, Suou caught a glimpse of the mysterious figure shown in the screenshot, which is apparently what everyone at school has been talking about.

In urban legends, the Hookman is a dangerous wraith, but he didn't seem to do any damage here aside from looking intimidating. I am leaning toward the usual "there must be a more reasonable explanation" routine that we have grown used to. I hope the upcoming deduction section clarifies things as Suou thinks it over, because honestly, I am completely confused at this point.

I don’t see anyone having a motive to fake being a wraith except perhaps Mayuri herself, who might want to scare Suou off. Suou ruled this out, however, because they were speaking just a moment before the appearance, leaving Mayuri no time to switch roles (she wasn't wearing that costume when the CG was shown). Hopefully this would also link to the Basquiat mystery that we are still searching an answer for.