Extra's Harem: Invincibility Starts with Marriage and lots of Children

Ryan, a normal office worker who could be considered an extra in a boring world, did his job regularly and spent time here and there.He found himself, by mistake, being killed by a female reaper. Yet, the only thing he received as justice was a chance to transmigrate into a new body with his memories intact.Meanwhile, that female reaper faced a very small punishment: her powers were suppressed for ten minutes, leaving Ryan with nothing but a mocking smirk from the reaper as she ridiculed him for being a meager human with no life that belonged to him. He was left with no choice but to stand in front of the one who had granted such "justice" and watch the reaper laugh while turning to leave the place.In front of him was the reincarnation pool, and beside it stood the woman smirking at his misery while completely powerless for a whole ten minutesthere was no justice for him here. With his hands clenched, he decided that if he was really going down, he would take her with him. Swiftly tackling her, he pushed the reaper and himself directly into the reincarnation pool.The next moment he knew, he found himself being born as a extra disposal substitute of the Ducal Prince, destined to die at the hands of the princess in his stead.Soon enough, he understood that instead of some random world, he had been transmigrated into the last novel he was reading and a fan ofInvincibility Starts with Marriage and Having Lots of Children.[ Disclaimer: First POV for main charcter is mixed in chapters with Third POV of other characters ]( Disclaimer: There could be mistakes in the chapters, not because I am weak in grammar or something, but when one has to write 8K a day, the chances of things being left out are pretty obvious. So, if you understand what that sentence means, just ignore the minor mistakes, but if you want to point out grammatical mistakes, please do so. I will correct them as soon as possible.)