Everyone gets an imprint of their soulmate's initials at the tender age of eighteen.. Marriage was usually decided on that. Keyword: was. The belief is a little old fashioned- only the older people of the 21st century pay it any mind while the newer generations? They ignore it to pursue their own love lives, the thought of being bound by initials rubbing them the wrong way. Izumo Arisu is a young girl who had suffered from heart problems for most of her life, and the only thing she ever looked forward to was when her soulmate's mark would appear on her eighteenth.. Only, it didn't. Arisu had been teetering over the edge between life and death for most of her life, so the norms of human biology wasn't the same for her. She didn't get a soulmate mark, instead, she finds herself slipping into something much more thrilling.