You can read this story on fanfiction .net. The author ist "Side-man". 33 chapters 142k words. Not sure if this is just a repost from the original author.
takumi_9800
Le gusta a personas 2
is this a Harem ?
Yes
Azathoth2:is this a Harem ?
I can't find it
Story was deleted and title changed along with the content. The one I was referring to is "Fate Akasha" by Side-man.