Just as there are men who get so tired that they end up with an 'exhausted dick,' is there a state for women where they become overly tired and easily aroused, making their vaginas wet? Women like OLs or female college students who miss the last train and fall asleep in a manga cafe while waiting for the first train of the day. If you approach them and touch their bodies, they will resist but still feel pleasure and give you a handjob. Then, once the woman is aroused, she won't be satisfied with just that and will seek sex herself...
