The girls definitely kill him every time he meets them. The sword lets you live for hours on end, and you still keep some level of control, if only for a while. Once he got far enough into the fight with the vampire girl, the sword completely took over, and he realized it was a dead end. So he moved on to something else.
He got possessed multiple times. After the first possession (when Judith said that "the main body's consciousness has already been taken over"), he said he "tried again and again without giving up", and that the possession "always happened". Which means it's more than once.
Ageha is literally the worst possible option. She remembers everything that happens, but only vaguely enough to be a hindrance to his attempts. It's literally the worst possible outcome. If she didn't remember at all, he could save scum her and reciprocate her affection. If she remembered more, she'd probably realize she killed herself, and the poor guy's only sin was not letting himself get raped.
I think "that girl" didn't actually remember though. It's just her 2nd personality (there's a chance that her name's not Ageha), which is totally different from the affectionate 1st personality (Ageha). That's why she had different attitude right from the start. Even at the end, rather than remembering anything, she just said that MC had a
bad smell, and she correlates that with "MC went against her in past life." Which is obviously wrong if she does remember. "There's no way she'd talk to someone like yourself," "Ageha refuses to talk to you," and "Don't ever get involved with Ageha" all points to a different, separate personality. Though I can't deny the possibility that the 1st personality did remember and hid from MC throughout the second encounter.