Setsubun was originally a term used to mark the days when the seasons changed from one to the next; now, the term is only used to describe the day before “Spring” in Japan. Setsubun usually falls on the 3rd or 4th of February.
Shoufuku literally means “inviting fortune,” and is used to describe something that brings about good fortune, but as the title is already so long, I’ve kept it this way.
Oni are creatures from folklore (you may see this alternately translated as “ogre,” “devil,” etc.); I’ve chosen “demon.”
(About the chapter title: Deep Love)
“Hiyoku Renri” (比翼連理) is also a four-character idiom, used to describe a couple deeply in love. This title becomes more meaningful in context when you understand the idiom. Hiyoku describes a mythical creature, hiyoku no tori, where two birds (one male, one female) have one eye (or head) and one wing each, and constantly fly as “one.” Renri refers to two trees (with different roots) growing close and merging.