"From secret spa girl to father-in-law's free sex-processing pet"

After Encountering My Hated Father-in-Law at a Men's Spa: I Became his Rejuvenation Massage Expert & Free Sexual-Relief Pet

The story follows Natsuki, who begins working at a men's spa to supplement her household income. Her secret is eventually discovered by her father-in-law. This discovery leads to a situation where he leverages this information to demand personal services from her, leading to a breakdown of their family boundaries.