Sara: We're all friends~ So, let's share MC-kun!
Nurikabe: Go to Hell--I want him all to myself!
Kou: I love that straightforward side of you!
The wall has declared her antagonistic stance in no uncertain terms, and yet those two are treating her like a friend. By canon, Sara allegedly has great perception, such that she can see through the deceitful; Kou is a strategist, and should have the brainpower to take apart the front that's right before her eyes--which isn't even much of one, because the wall isn't hiding much.