There are multiple timelines, and in all of them Chloe starts off as a normal human.
At the start, Chloe sees Mea being bullied and follows her to a playground, but can't find Mea here. The guide succubus (the new one wearing blue) appears + pulls her into the succubus world.
Chloe, controlled by the player, must progress through the game while resisting the temptations of the succubi. If she reaches Lust Reaper and manages to beat her, she's returned to the human world. She sees Mea, but Mea teleports away in the same manner as the succubi... I'm not quite sure what this means. Afterwards, the guide reappears and talks about how this timeline has a happy ending, then bids the player goodbye and tells them to play with the Chloe of another timeline.
If Chloe loses to Lust Reaper twice, she submits to pleasure. Lust Reaper erases her memories of being human and transforms her into Manuve. The guide appears and explains how this is Manuve's backstory, and also how she'll eventually meet a human boy (an obvious reference to Magrut + Lust Grimm).
The guide succubus is 62studio's mascot, originally introduced in
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. I think she calls Chloe "senpai" because she knows of her future as Manuve. She'll probably appear in future games like Succubus Puttel.