Its because his been taking birth control and heat inducers for to long those have side effects and caused difficulty getting pregnant or make you unable to. Its sad cause i want them to have babies (︶︿︶)=凸
I think it is chapter three when they meet Keisuke's dad. Karasuma used and abused birth control drugs and so his body is not equipped to carry a child. It is unclear if he will be at a better state to have one or if it is permanent.
Anyone know where can I read the raws?