Uchi no Ichizu na Tsuma ni Kagitte... ~Jitakunai Netorare o Misetsukerareru Otto~

One night, when I was tired and immediately fell asleep... "...*slurp *suck..." ...I woke up after hearing strange noises. I'm not sure, but it sounds like someone's voice. However, I'm sleepy. After all, I'm exhausted. That's why I ignored it and decided to sleep. I slowly closed my eyes once again, and tried to surrender my consciousness to the comfort of my bed, when... "...*pant *gasp... Nee-san..." What? "Ahn jeez, I can't swallow it all *slurp *suck..." That was the voice of my wife Nanao who is supposed to be sleeping beside me, and the other was the voice of her little brother Eisuke. What on earth is happening? What is Nanao and Eisuke-kun doing? Firstly, are those really the voices of Nanao and Eisuke-kun? While confused, I slightly opened my eyes and looked at the direction where the voices are coming from. What I saw was...