Akai Ito

The film takes a simple idea—creating a picture using a simple thread—and transforms it into an engaging flow of animated images. From East Asian folklore, Okushita takes the symbol of the red string of fate. There are many variations of this ancient tale, but the main idea is that the gods tie men and women together who are destined as each other's soul mates together with a red thread.

An invisible red thread connects those who are destined to meet,
regardless of time, place, or circumstance.
The thread may stretch or tangle, but it will never break.
-ancient Chinese belief

(Source: myanimelist.net)