Iku was the one who was betrayed the most this chapter, that sorrow and betrayal on her face can be discerned without any doubt. And to think Mei of all people would be the one to do it.
To be fair, the ones in the background/periphery of the big group shot are the ones who were in maid uniforms way back in the maid squirt gun battle chapter. So I get why they're not double-dipping.