https://www.dlsite.com/maniax/work/=/product_id/RJ01469020.html
https://www.dmm.co.jp/dc/doujin/-/detail/=/cid=d_664633/

[Synopsis]

Chikako Kodama begins living alone to attend university, starting a long-distance relationship with her boyfriend, Haruki Hamatani.
She attends a university welcome party but feels out of place and tries to leave.
However, her senior, Yuji Amaya, drugs her with a sleeping pill and puts her to sleep.
When she wakes, she finds herself naked on a bed, her body being ravaged.
This single day drastically changes her life.
Unable to resist the senior, she descends into a daily routine of sex, becoming nothing more than a fuck buddy.
Unable to confide in her boyfriend, she struggles alone.
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Enjoy watching her struggle between the pleasure of sex and her guilt towards her boyfriend!

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