Now that we know Slenderman has thought about taking on Takehashi's appearance, I wonder if he has resorted to psy ops by imitating Takehashi to turn Itou against her. It could be that the murder last chapter was done by Slenderman or someone else and Slenderman decided to pin it on Takehashi.
At least I think that's supposed to be Takehashi in the last panel in 15, unless I'm forgetting some other character. It's a much more Slenderman like pose and expression, with no worm in sight.
With his history of successfully replacing people after imitating their appearance, he does have a bias here that could lead to him overstating the importance of appearance.
Of course, appearance is much more important than most humans would admit. That would fit the "cynical but not entirely wrong monster takes on social relationships" motif we got from Takehashi.