https://www.dlsite.com/books/work/=/product_id/BJ023049.html
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Sibling Sex Education - I lust after my defenseless younger sister

A brother and a sister are drowning in a forbidden relationship!
The younger sister's body, which has grown up to be a woman, makes the older brother's rationality collapse!
The Haruhara family is without a mother since their parents divorced. Father is often away from home, and the older brother, Takahiro, a college student, is busy with housework and part-time jobs.
However, his younger sister, Akina, does not help with the housework and acts uninhibitedly in revealing, unprotected clothing.
One day, Takahiro happens to see his sister naked, and he feels a woman's desire for her, and although he is confused, he is excited...!
That night, Takahiro comes home drunk and peeks into Akina's room...!

兄妹性育～無防備な妹に欲情するオレ(1)
https://www.bookwalker.com.tw/product/62030
forcs版的好像畫質好很多

Base +6