Wow, this is pretty similar to "The Princess in the Dumpster", just that the Mc doesn't turn back in time in this story ヾ(❀╹◡╹)ﾉ~
This is something you would expect from scam not the duke
（￣へ￣）
wait but whats the point of him going back if he cant remember anything?
wow same method as IRIS - Lady with a Smartphone
She didn't trade her memories though...did she?
Ask him and the author who though this arrangment ╮(￣▽￣)╭
He must have thought that he would rather want his daughter living her life fine somewhere in the world instead of letting her die while he made the decision(save his daughter but have no recollection of his daughter and wife).
in exchange for his memories of his daughter with is the MC and his wife, the MC will live again
they're not siblings, mc is actually the dukes daughter, there's actually a reason why the duke forgot her
x x S P O I L E R S x x
the MC actually died in an house fire at age 18 if i remember it correctly, i dont know who the duke made a deal with, but he exchange all his memories of his daughter and his wife so he could return to the past, with is now and he wouldn't get back his memories