Goeyeon

Yeon-Woo, the son of a hero who protected the country, is the number one candidate for groom among the village girls because he excels in both scholarship and martial arts. His only worry is that his lower body cannot stand due to erectile dysfunction. In order to solve his worry, he hears a rumor about a rock that grants wishes and climbs up the mountain behind the village, where he finds a young man being raped by a monster. As he hurries to save him, Yeon-Woo notices something wrong with his own body first...! "Why is it standing up all of a sudden?"(Source: MrBlue, translated)