Onedari Sweetie ~Koi no Oironashi wa Nando de~

Minakami Shuusuke is a cute guy, the kind that stimulates women's maternal instincts. He falls in love at first sight with his homeroom teacher, Ayase Yuzuha, and they start dating. Shuusuke's cousin, Fuyuko, is a popular cosplayer and so, she tries to introduce him to the world of cosplay, but he can't even pretend to be interested. When she hears about his girlfriend, Fuyuko comes up with a plan. She gives Shuusuke one of her outfits and tells him to make his girlfriend wear it. Now that she's got him cornered, he reluctantly agrees to do it. When alone with Yuzuha, he asks her to put on the outfit. Flustered, Yuzuha initially refuses. After some pleading, however, she gives in. The look on her face as he begged made his heart beat faster. But the embarrassment written on it after she changes into the outfit is even more exciting. He can't hold himself back anymore, so he pounces on Yuzuha and they have sex right then and there. That reminded Shuusuke just how fun it is to tease Yuzuha. Whenever he asks her to do something lewd and gets to see that flustered face of hers, he gets extra hard. Since that day, Shuusuke and Yuzuha are all about cosplay sex, and they don't even realize it was all Fuyuko's mischievous doing...

[Translated from official website]