The Perfect Plan to Avoid the Death Ending

Reincarnated as Sienna Winter, a minor villainess in a novel who has a terminal illness, she sets out to avoid the death ending and survive. But her plans take an unexpected turn when she accidentally awakens a sealed demon named Helares Eckbert, who claims she is the one who awakened him and calls her his master. Sienna then finds herself caught in a fraudulent contract that lasts until she dies. Since she is already terminally ill, she must figure out whether she can survive the situation she has stumbled into.