Faced with two equally unfavorable choices, Number 6 sees little in the way of options. Unless he physically restrains this boy, that knife is inevitably coming out.

"Fine, but I'd still like to insist that this is a bad idea. Brace yourself." He'll give Natsuno a moment to prepare, and then he will grip the knife handle and pull in one quick clean jerk of motion. This is, unfortunately, not the first blade he's pulled from a person.