Its delusional misidentification syndrome, specifically capgras delusion, which someone hold a delusion that a loved one has been replaced by an imposter. Usually they think it's an doppelganger, or some stranger in disguise, but sometimes they also think it's an alien, shapeshifter, monster, ghost or something along that lines.
Or maybe, he used himself as a test subject for project apple and gain some superpower. But Melinda think the changes is because he is replaced by an alien.









Ukh... I always hate this kind of harem. Some korean author really like trope "bunch of young barely legal girls obsessed with much much much older man who think she's his daughter or student".
I bet all his "daughter" also will in love, obsessed and will do anything for him.
Its not a harem. There's not even meant to be romance between any of the kids from what I've heard, MC doesn't think of them as any more than kids and does not end with them.
Just because he doesn't fall in love with one or more girl, it doesn't mean this is not harem. The three adopted daughters, two noble ladies, two girls from magic tower. If every important characters is girl, everyone blushing when they see him, wearing unnecessary sexy clothes and do unnecessary sexy poses, you know it's harem story.