Life with my Little Sister

When I realized, it was a different world there. The protagonist, who was a Japanese salarier, was a baby when he opened his eyes. Apparently, I was reincarnated into another world after I died of overwork... Born in an aristocratic house, the official status was that of a civilian, since his mother was a concubine. Such a protagonist can have a presence that he wants to protect over the course of his life. A real sister, born of the same mother. And my sister, she never seems to want to let go of her brother...? The life of a reborn who lives with his beloved sister begins.