Chisame whores herself disguised as the other girls (mostly Asuna) in order to ruin their reputation because their fansites (made by Kamo) were stealing Chisame's 1st place on the internets. Eventually her mind snaps from too much whoring and she starts believing she is the real Asuna. Asuna and fake Asuna confront each other, Negi tries to stop them and gets stabbed
. I haven't seen volume 5 yet.