After a long week apart due to conflicting work schedules with his girlfriend Haruka while living together in Tokyo-style apartments (implied), Yosuke is desperate for some quality time. Haruka agrees to let him take her whenever he gets home from work. When Yosuke returns to find his girlfriend asleep in lacy lingerie—a sight that immediately drives him wild—he can’t wait another moment to relieve his built-up tension.
As he dives into passionate lovemaking beneath the covers of what he assumes is Haruka’s body under sheer panties, he finally catches sight of her face: it’s Kanon-chan! It turns out Kanon is hiding out because she had an argument with their mother earlier that day. Luckily for Yosuke (and poor Kanon), she won't be around much longer; she heads back home the next morning, and Haruka promises to make up for this hilarious mix-up.
The accidental encounter doesn't end there. Later, Yosuke sees a nude woman wrapped only in a towel emerging from the bathroom. Assuming it must be Haruka returning from her errands, he eagerly rushes over to claim his reward. But just as pleasure peaks, the towel slips away, revealing not Haruka, but Kanon herself! In a rush of panic and excitement, Yosuke loses control completely, flooding his entire load deep inside his girlfriend's younger sister.