When Cheonggyecheon Stream was covered, Yeon-jun, who had escaped, is actually a crayfish who has transformed into a human. Yeon-jun hides in the Cheonggyecheon aquarium street, protecting creatures in similar situations and hiding around Cheonggyecheon. Yeon-jun maintains eternal life through repeated molting, but as he molts more, he begins to doubt eternal life. Then, Yeon-jun meets and grows close to Ju, a regular customer who resembles his daughter. Upon learning that Ju's life is nearing its end, he contemplates giving up his eternal life for her.