Plez Halp

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I've been looking for a manga/hentai on and off for a couple years. I can't for the life of me remember the name or author of it.
I read it quite some time ago and can remember a relatively decent amount of information from the story.
It's a bit vague but i'll do my best.

So we begin our story with a pretty average male lead running from some guys in black.
For some reason he is in an area with shops, possibly a mall, I don't remember. So he ducks in this shop to escape the guys.
Lo and behold it's some kind of Magic shop and there's a blonde there (I believe she has glasses) and long story short he begins working there as her assistant.
She does some crazy experiments sometimes iirc. They fuck every now and then and develop a relationship.
Anyway, for some reason this organization is after him for a reason that is never explained and eventually some dark skinned girl comes along
and she's arrogant and get's trapped and he ends up fucking her.
I remember specifically her "silver pubes" being mentioned.
So that happens and I don't remember if she sticks around or returns to her organization but, they go on their merry way.
Until, the blonde magic girls "teacher" comes into the picture and captures them both at some point and is trying this whole eternal youth thing or some shit.
Anyway, they overcome this great challenge with the power of their love yadda yadda and they live happily ever after.

Any thoughts?