anon funnily enough i have a very certain answer for this because i love an active reactor -which is iku. i LOVE and enjoy writing jealous iku so much, it's like butter on my crisp bread, it's the air that i breathe. it's also beautiful to witness, because iku's jealousy has almost no bounds, he literally makes sure you KNOW he did this with jehi, he bought that with jehi, he ate and experienced the most with jehi. for iku, there are no limits to his possessiveness which i find so beautiful in him.
however, i also want to add that the way jealous jehi moves when he is jealous is quite astonishing. because it hits you at the moments you don't expect, at least for me haha. dy has that calm and collected stance when it comes to his own reactions over relationships/situations outside of the grp content sometimes (if ykyk) so i think that is why when we see a glimpse of his jealousy, it is just soooo delicious it makes one feel so excited after not seeing it for so long. it's almost like he freezes and keeps looking at his target quietly which makes him look so musowooo -i get riku i really do! and i also really like the way he keeps an eye out on what iku is doing in his viewpoint, like a protective stance in the corner of the frame, which also makes me feel giddyyybkbkdfh