Idk why people are saying it's an alt story when nothing says it is. And also in DLsite (Yes i know it's MTL but still) :
The only thing said here is that you don't need to play the previous work to understand, since in that game you're focusing on saving the sister. (Was going to say the virginity thing could make it not canon, don't remember if after Last Embryo you can choose if Claudia is a virgin or not and don't know if in Ark of Artemis (or even Ultimate Angel Zerachiel) there's a canon event where she loses her virginity or not. Could change things.)
Even in game they're talking about how she's the one who saved the continent.
Well. It could also be an alt story, depending on what's said in the games. At the moment i didn't play Ark of Artemis or Ultimate Angel Zerachiel yet, only played Last Embryo, so idk if in Ark of Artemis or Ultimate Angel Zerachiel it's said she wants to save her sister at some point. Also idk if in Ultimate Angel Zerachiel her sister has already been saved or not so yeah. (Saying it like that because timeline wise ain't sure how it's placed)
I do remember seeing somewhere that the timeline of games was posted at one point, tho i don't remember where.
Only thing i know about timeline is :
Last Embryo -> Ark of Artemis -??? How to Create a Witch (Just don't know which one happens first)
-??? Ultimate Angel Zerachiel
Only game i know that doesn't matter timeline wise is about the red aired angel keeping company to a boy since not much happens in it as far as i know.
Is there only one ending and is it a Bad/ Sad one? Ark of Artemis ending ended on a hopeful note to the heroine.
Only one ending and don't worry, it ends well