Nitou Ou Mono wa Ittou mo Ezu

You are a feudal lord in past Japan. You don't have a successor yet so lots of girls go crazy about you. They pull down their panties in front of you just so to have the chance to bear the next ruler. Frenzies of raging princesses that compete each other for your seed is a norm around your castle. Reverse rapes are common as well. Yet no one has ever been able to bear your child. No, no one has ever been able to have sex with you... Because you are an impo.
One day, just as usual, girls are introduced to you in the hope that their gorgeousness might cause your little limpy to go stiffy... Instead of meeting a girl, your vassal introduced two katanas named Kotetsu and Muramasa. And right when you touch, the blades transform into girls...

(Source: Kaorinusantara)