I'm the Corrupted Side Character's Wife

Lucian Kardien—he was the hero who led the war to victory. He was the second male lead who loved the female lead so much that he turned yandere. And I'm the fiancée who will be killed by his hand. Of all things, why did I have to transmigrate here! I must somehow increase his likability to prevent a "surprise" ending. With a toothy grin and my clapping hands of approval, I'll help him connect with the female lead! But what is this reaction? "Lady Pernia... please don't provoke me anymore." ...Why is it still a scary ending?! (Source: Delphiniue, translated)