so i'm about six chapters in, and I'm starting to speculate how the love potion works here.
with tsubasa it seems like she's the purest one with the reaction she got from the potion. we're not even sure if the effect even wore off by now or not.
and with the previous girls, they remembered the events after, and despite the potion wearing off, they all seem to actually like itsumi.
However, itsumi doesn't seem to still have a crush on ruruka after the effect wore off on her, so this leads me to two different ideas.
1: the love potion brings out the user's inner feelings of the person that gave them the potion, and whilst that effect is strong in the beginning, it still persists once the effects ware off, meaning that the subjects had feelings for the person before they drank the potion and the potion just sped up the process
2: the love potion is still in effect for the ones that drank it, but if they are aware of the potion, then it doesn't work. Itsumi doesn't seem to share any of the same traits that the others have when she's around ruruka, so I'm guessing she hasn't noticed yet or the potion doesn't work properly if the consumer is aware of the potion.
i won't know for sure, but there's several more chapters ahead, so I'm looking forward to it