Hmm... From past strips, I know that Chen is Franklin and Nue is Lydia (a minor early-'90s character), but Koishi has me stumped. It's like I can just about think of who she's supposed to be, and I'll probably end up kicking myself once I figure it out, but for the moment I'm drawing a blank as to a name. The characters in this series of images are those who are definitely supposed to represent actual Peanuts characters, too, so that's not simply a case of Chamupei rendering Koishi in Schulz's style.
Any takers? (I almost want to say Eudora because of the hat and the hair, but that doesn't seem totally right either.)
My thoughts on this one is that Koishi and Nue are Patty and Violet here (even though Nue is Lydia elsewhere)... its just the vibe I'm getting off them.