The protagonist, Naoto, and his girlfriend Yurika have been in a relationship for a year without even kissing each other. One day, Yuriko's grandfather showed Naoto a smart phone application, which is a game with an objective to "capture" Yuriko. Yuriko's grandpa claimed that he has no idea who created the application, and asked Naoto to protect Yuriko. The game has several "missions" and the first one is to kiss Yuriko. Several male students at school have seen the same app and all of them want Yuriko. Of course, the missions became more bold and indecent as the game advances.

Will Naoto be able to protect his girlfriend from those guys? Who created the app? Will Yuriko remain in a relationship with Naoto even after being forced to have sex with others guys? You need to play to find out.

[Edited from a description by FHC]