Before arriving in Japan, the concept of the red thread of fate originated in Chinese folklore as the ‘yinyuan hongxian’ and is associated with the god Yue Lao, the ‘old man under the moon’ who presides over love and marriage. He is said to carry a book listing the names of couples and ties together the ankles of people fated to be married with paradoxically red, yet invisible, cords/threads that stretch through all times and circumstances without breaking.

There are many variant stories in folklore surrounding Yue Lao but the most famous involves a young man named Wei Gu who comes upon the god in the form of an old man who is reading a book by moonlight in the city of Songcheng. After Yue Lao reveals himself, the ambitious young man demands to know who his wife will be, hoping to marry into a rich, politically connected family. They later meet in the marketplace where Yue Lao shows Wei Gu’s thread connected to a poor, three-year-old girl who is being carried by an old blind woman. Shocked and angered, Wei Gu orders a servant to kill them.

Years later, Wei Gu has become a public official and marries the daughter of a governor. She is beautiful and kind but mysteriously walks with a limp and always covers her forehead with a silk band. When he questions her about her injuries she breaks down and reveals that she was actually the niece of a governor who lost her parents when she was young, growing up with her old blind nanny, the same girl and old woman that Wei Gu had ordered killed years ago who only narrowly escaped death herself. Overcome with guilt, he confesses that he was the one responsible and begs for her forgiveness, which she gives revealing Yue Lao to be right in the end.

Other variants of the story are more tame, having the two meet as children but have the boy only tease or throw a small rock at the girl but all ultimately see him forgiven by his—extremely gracious—future wife.

Like many myths, traditions, and cultural institutions originating in China, the concept of the red thread of fate eventually made its way to Japan where it would take on a few new characteristics along with its own variants on Wei Gu’s story. Probably the biggest difference in the transition involves its placement, which is traditionally said to be tied around the thumb of the man and the pinky finger of the woman but has now further evolved to typically be on the pinky finger of both partners.

While, for the most part, the specific association with Yue Lao and Wei Gu seems to have gotten lost in translation over time, the red thread has proved to be an enduring cultural symbol in Japan, appearing frequently in pop culture media, especially in shoujo manga and dramas. Perhaps partially because it has been distanced a bit from its religious origins, it is also often parodied such as the Haiyore! Nyaruko-san’s “red tentacle of fate” or Tenchi being comically connected by many strings to basically every major character in the harem series Tenchi in Tokyo.

While the concept of fated love, and fate in general, is quite widespread in anime, it seems the thread itself being visualized is most commonly seen in opening and ending animations such as in Hibike! Euphonium’s first ED "Tutti!", Potemayo’s OP "Katamichi Catchball" (where it is specifically mentioned in the lyrics), and the final shot of Inuyasha: The Final Act’s first ED "With You".

That’s not to say that it doesn’t appear in one way or another at all, though. One of the more dark and interesting variants on the red thread is seen in Jigoku Shoujo (Hell Girl) where the clients can summon Enma Ai, the titular hell girl, to send those who wronged them to a torturous afterlife, but only after seals their contract with her by untying a red string, condemning themselves to the same fate after they die.

Other references to the red thread include Kuwabara claiming he found his love interest Yukina by following the red string tied to their fingers in Yu Yu Hakusho, Index guessing that perhaps the reason so many girls are interested in him is that his magic-nullifying ability Imagine Breaker is cancelling out the red threads of others, the red bracelet and hair ribbon of the main characters in Kimi no Na wa. (Your Name.), and possibly the life fibers prominently featured in Kill la Kill.