"I", Marle, was reincarnated as a boy in another world. He woke up with his memories unclear... in a vast dark forest!?At that time, he met Illtimina, a beautiful demon hunter and female adventurer. By chance, he saves her life, and he is followed by her, and at the same time, he sets out on a journey while being protected by her. Thus, Marle's adventure and her journey to another world begin in order to someday become a full-fledged person worthy of her! An age difference adventure fantasy where you go with the beautiful and strongest older sister!