The real enemy was my older brother.

A duke's daughter and a commoner. Even such a difference in status was resolved through the battle against the Demon King, and everything was going smoothly. We were counting down to our engagement——or so I thought, but my older brother opposed it. For a completely unreasonable reason. / This is the story of Cain, the older brother from "It's All Pretty Much My Brother's Fault," and the holy maiden. Planned as two parts. ※There is a risk that the image of Ian, the hero of the previous work, may be damaged.