No one uploaded it after years so here it is, I assume it's because every bulk upload the author does is missing it for some reason? Even though he released this https://www.dlsite.com/maniax/work/=/product_id/RJ316923.html 3 months ago even?
Chapter 7: https://www.dlsite.com/books/work/=/product_id/BJ197425.html
Chapter 8: https://www.dlsite.com/books/work/=/product_id/BJ237338.html

Chapters 1-3: https://e-hentai.org/g/1266497/474581b786/
Chapters 4-6: https://e-hentai.org/g/1374192/3abb64986d/

EDIT: Actually the title is 俺の初恋相手だった義妹が親父と種付けセックスしていた件 7 & 8 but it's clearly a direct continuation of 俺の大切な幼馴染が親父のセフレになっていた件, no idea, not included in either bulk. Looking further 俺の大切な幼馴染が親父のセフレになっていた件 is just chapter 4-6 of 俺の初恋相手だった義妹が親父と種付けセックスしていた件 on dlsite, this being 7-8. Perhaps 7-9 is supposed to be something else bulk uploaded and the previous title is a lie because the content only happens in 7-8...

Damn, didn't know chapters were out, thanks for the upload!

Base +6, Gabygabycandid +6, f2faaam +6

[アイアンシュガー] ナマイキな妹が俺のセフレになった経緯The 48th cg without text of this book is wrong...Who has the right one?????

Base +6