The series follows Saki Watase, an office lady who takes a side gig reviewing products to make ends meet. She's shocked when the first product is a box of XL condoms, a size she has no use for. After a night of drinking, her demanding and intimidating boss, Keisuke Sudou, discovers her secret job. He then reveals that he's packing an enormous, XL-sized cock and offers to help her with the 'product testing.' This kicks off a series of intensely carnal encounters. Saki's initial apprehension melts away as Keisuke repeatedly fucks her in various positions, from her desk at the office to his bed at home. He relentlessly pounds his massive dick deep inside her until she's screaming his name, her body convulsing in orgasm after orgasm. The narrative focuses on their escalating sexual relationship, exploring how Keisuke's huge cock stretches and fills her completely, turning their professional dynamic into a raw, fuck-fueled romance where he takes her whenever and wherever he wants.