https://www.dlsite.com/books/work/=/product_id/BJ325266.html

Public harem of cuckolded sisters

My best friend's younger sister is a hardcore, ultra-bro-con.
When I made a bunch of flowery and beautiful speeches to her about how I was doing it for her brother, she readily accepted me.
After that, I called her every day after school and disciplined her thoroughly until she had the body I wanted.
I even took my best friend's older sister and put my poisonous fangs on her.......?
I'm going to enjoy the pleasure of cuckolding his beloved sisters!

Base +10, yupokamusi -8

Oh! Sisters NTR is a little rarer, I remember [Carn] Otome Netoria - Maiden NeTRia as the one I like the most.

Base +14