Firstly, I can't believe I binged this absolute train wreck of a manga. Secondly, killing humans doesn't give XP. Only monsters and our erstwhile protag piñatas do that. It would be kinder to have finished her off, but it's more fitting vengeance to leave her to rot. She's been completely neutralized anyway, since she's not getting any of their blood to rejuvenate herself anymore. The blood she (pointlessly) collected in reserve is useless because it has to be fresh, and even if it didn't, Haruto has zero interest in bailing her out or putting her out of her misery. I'm just over here wondering how she didn't make herself violently ill from drinking that much blood. It would be minutely more forgivable if the blood gave her youth, but she paid for it in stomachaches and vomiting. She was already shown to have the willpower to take ten times what she dished out if it meant staying young, even if she really would rather not have, so a little inconvenience like that would be nothing. But nope. It's magic. Lastly, I'll see you all next chapter. Dangit.