My Handsome Senior Brother, His Junior Only Wants to Steal Him Away

[Two male leads, a touch of yandere, villain, happy ending, sweet romance] Gu Yuanjun transmigrates into another world, waking up to a whole new life. But it's no big deal. A wage slave is a wage slave wherever he goes... He takes on a mission, thinking all he has to do is coast through the plot. Who knew it would be like peeling an onion, layer after layer? He was handed a disposable side character's script, but somehow ended up following the villain's path. Gu Yuanjun is exhausted. And his adorable junior brother's personality keeps getting more and more twisted: a loyal underling, a deranged attack dog, even a clingy crybaby puppy. He switches between them seamlessly. Gu Yuanjun: “...” “Senior Brother, if you ever abandon me again, I'll lock you up so you can never leave...” “Big Brother, A Yi will be good. Please don't leave me, okay? *Sob*...” Gu Yuanjun is at his wit's end. Let go, let go of me! I'm the villain. I'm supposed to destroy the world.