So it looks like the whole thing takes place during the Groundhog Month, since Homura is apparently a magical girl. Mami meets Charlotte but survives her. What's weirder is that Kyouko's apparently in Mitakihara (although we only see her and Mami interact in the third chapter, so it's possible Kyouko came here in search of Oriko). Madoka and Sayaka remain in ignorant bliss, and Homura seems to behave like a watchdog for every magical girl trying to approach them even accidentally.
It's hard to say if we'll get info on Walpurgis Night (it should be existing already, so it doesn't seem to be Oriko, Yuma etc.). Oriko apparently foresaw Gretchen's birth and tries to prevent it. The methods, though, are still unclear - why does she use Kirika to kill magical girls around, but makes Yuma contract? Of course, seeing what grief Yuma burdens, her magical power as a Puella Magi and a consequent witch shoudl be significant... but then why have her become a magical girl in the first place? Maybe to deal with Walpurgis Night so that Madoka doesn't have to do it? But instead of killing a whole crowd of Puellae Magi in Mitakihara, wouldn't it have been better to team them up and outnumber WN?
Oriko's intentions are really a mystery...
Also, this incident practically left the city without magical girls right before WN's arrival. I find it strange how Mami and Madoka wouldn't have noticed it in earlier timelines (not speaking about the consequent ones, since Homura might have known it already and done something about it). As Madoka had already contracted before, she should have been Oriko and Kirika's target in the past (if Oriko's visions featured her at all, of course). And if the accident only took place in this timeline, what exactly could have Homura changed to cause this turn of events? She's the only one who seems to bring turmoils to the course of time.