I'm the Corrupted Side Character's Wife

What would you do if your fiance holds the demon's power inside him and could kill you with it? The answer is clear for the reader who wakes up as Lucian's fiancee, Pernia. That is, she must help Lucian confess to the novel's heroine, Estelle, so his unrequited love won't trigger the demon! Whether it's teaching Lucian to dance or inviting Estelle to her own engagement ceremony, the plucky Pernia is willing to do whatever it takes to get them together. So why is the deadly Lucian turning his eyes toward her instead...?