Chu Shite Agechau ~Oshikake Onee-san no Seikou Chiryou~

I, Segawa Akira, am a normal boy who attends a normal school.
Besides my mother, I have two older women I've known for a long time, or rather, who I know well.
One of them is Hinomiya Yuu. I call her Yu-nee.
She's a teacher, but she's always kind and supportive, like a big sister to me.
The other is Takamori Sana. She's a childhood friend, a year older than me, and I used to play with her a lot when I was a kid.
I lost my father before I could even remember and don't have any siblings, but thanks to Yu-nee, who looked after me like a younger brother, and Sana, who was my playmate, I never felt lonely, even though I was young.
However, perhaps because I was always surrounded by them, I didn't have much contact with other boys.
Perhaps because of this environment, it took me a while to realize that my body was different from the other boys.
A physical examination at school revealed something strange about my body. Eh... Does a penis grow hair...?
Could it be... that I, uh, masturbate? Because I've never masturbated!? (No.)
After consulting with my older sister Yu, I was taken to a hospital where a beautiful and seductive female doctor works.
The doctor, who introduced herself as Tachibana Kimika, gave me some shocking results.
What?! If this continues, I might lose my manhood (penis)!?
That shocking revelation already broke my heart, but the treatment plan was even more unprecedented.
To keep having sex with women!?
And when my mother heard that, she said something completely off the mark: "You have to use proper birth control!"
No, no, no, I don't think that's the problem...
And so, a completely different, extremely exciting life began, completely transforming my mundane days...