Responses
From the hints ive gotten from the story and inturactions we've had with him I think he's obsessed over her because he made her cry a long time ago when she had to "kill" her other brother agin but in illusion form and since he hasn't seen her cry since he's become obsessed with trying to make her upset and cry. Kinnda like heras from "when a villaness loves" but way more sadistic and unforgiving.
Why do i have a feeling that her older brother will suddenly appear and ruin their plan ( ̄へ ̄)