Minase Haru was in love with the the school's idol Minase Kaoru, who also happened to be his older sister. However, in spite of that, he just couldn't be honest with himself and regretted it every day.

Due to a certain event he found out his sister was actually his brother, cross dressing.

"But I loved her even though she was my sister!"

After hearing that Kaoru accepts all of Haru's feelings........
And the two throw away the boundaries and flirt with each other endlessly.

Where exactly are the siblings going?
To go have sex in cosplay at school of course.

Haru gradually awakes to the joys of traps......