Flirty, handsome high school student Daiki has one defining trait: his self-professed sister complex. In Daiki's eyes, his beloved big sister Futaba will always be number one and deserves nothing but the very best - so who is this Kamiya guy, and why is he hanging around with her!? Thinking that no way in hell is his sis hooking up with this gloomy dude on his watch, Daiki sneaks into her college and confronts Kamiya. It turns out that Kamiya isn't Futaba's boyfriend, but one thing leads to another, and he becomes Daiki's friend. The more they hang out, the closer they get until Daiki realizes his heart skips a beat whenever Kamiya flushes red.