Akira Wakatsuki was coping with a serious day-to-day struggle.
His father had recently passed, leaving behind a gorgeous second wife, Manami,
who brought her hot daughter Karen to live together with Akira under one roof.
Manami has been showering Akira with love regardless of the fact they're not actually related,
meanwhile Karen does him favors with a playful and happy air.
To put it bluntly, Akira is attuned to their womanhood.

No, that's too tasteful. Akira is horny for step-mommy and step-sis.

Akira starts his day fapping to them before breakfast.
He surges dizzily at the sight of Manami's ripe, sweet full body and
Karen drapes herself in casual clothes that accentuate, not hide, her sexiness.
He can't take it. He's constantly ready to blow.

That's when Akira discovers an unusual eye dropper among his father's things.
His father had been a scientist -- who did very unusual science indeed --
and before his life was ended by that deadly anteanter attack in Honduras,
he had shipped a strange synthethic drug back home.