The Seme is so fine, though it's a webtoon but whenever he smiles it looks like he's really happy and satisfied seeing UKE getting pleasure which is basically a plus point and I don't think Seme's behaviour Psycho, it's more like he feels happy in giving out the things and he must've found UKE miserable and I hope they switch one day UwU (╥﹏╥)
Well in old times, it was no surprise to get married to your first cousins, and Hari was a child raised by the Duke family (and I don't think they adopted her somehow or whatever) and Eugene wanted her to treat like his sister but couldn't and was forced by the feeling and also Hari's. And I think both of them developed feeling for each other.
And K think the main motive of Hari coming back to old self is to sort out all the buried feelings. You must have seen Eugene in 1st panel glancing at her from the door. I think there must be something related to that.
And didn't we all see how people also were aware of the fact that she's not their real sister, and Hari all this time tried to be their sister though she was never asked how she felt. So I am rooting for Eugene and Hari if they clear all the misunderstandings.
Wow that 12 year old girl is catching boys like Poke balls, and here I am at the age of 20 eating Whoopies.