So, uh, nothing to do with the acfual story plot, but about the Genji plan. It's called a "plan" because it's not just "a man happens to fall in love with his adopted daughter". It's literally "a man adopts or becomes a guardian to a younger woman with the purposeful intention of marrying her later".
It references the protagonist of Tale of Genji, Hikaru Genji. The way it works in the novel is wild. Hikaru Genji is in love with his stepmother, but was refused. Then at some point he sees Murasaki, a young girl who looks a lot like his stepmother. So he decided to "adopt" the girl, with the intention of making her his wife. To make things even more insane, Murasaki is actually a relative of the stepmother that Genji was attracted to, which explains the resemblance.
The author, who is a woman, apparently intends this to be actually seen as a romantic development, but well... It's worth noting that even in the novel text itself the other characters thought it was weird that Genji (who was 18) is interested in a 10 year old girl, and her grandma even literally said "let's wait a few more years".
Anyway, putting this as a reference like this kinda makes the MC's situation of being mistaken for a kid just even more not funny IMO.