Zonshen's granddaughter. For as long as she can remember, she has been obsessed with hide-and-seek. Yilin has been known to stay in hiding for days at a time, so challenging her requires a special kind of fortitude.
— Directory, Sonic Unleashed
While living in her village, Yilin loved to play, especially with her grandfather, Zonshen, where she could play hide-and-seek for days. Whenever Yilin became sick or needed treatment, Zonshen would personally treat Yilin by giving her special medicine and secret treatments. Yilin, however, always thought that her grandfather's medicines were bitter and that his treatments hurt.
During the events of Sonic Unleashed, Yilin learned that Zonshen had gone missing when looking for the village treasure, and became both worried about Zonshen safety and sad for losing her playmate. When Sonic the Hedgehog and Chip later arrived in Chun-nan, Yilin told them about what had happen to Zonshen before asking Sonic to bring Zonshen back for her. When Sonic and Chip later found Zonshen and returned with him, Yilin expressed to Sonic how glad she was to have Zonshen back home.
Not long after, Badniks appeared outside Chun-nan, where Yilin personally saw them herself and was scared out of her mind. When Sonic and Chip later returned to Chun-nan, Yilin told them truthfully about the robots. After Sonic returned from fending off Eggman's robots, Yilin told Sonic of how amazed she was at him. As she thought about how Sonic always appeared when there was trouble, Yilin compassionately told Sonic that she loved him. As Sonic and Chip left Chun-nan, Yilin became worried that Sonic would forget them and never come back, but was overjoyed when she saw Sonic coming back, where she told Sonic that she loved him for coming back.
When Sonic sought Zonshen's help to cure him of his Werehog form, Yilin and Chun talked with Sonic about how Zonshen was a famous doctor, to which Yilin agreed with Chun about their grandfather. However, as soon as Chun claimed that it was thanks to Zonshen he was hearty, Yilin disagreed, saying that he was just fat. After Sonic had gathered the herbs for his cure, Yilin and Chun noticed how much fun Zonshen had making the cure for Sonic, and later passed this information onto Sonic and Chip, where Yilin remarked it was peculiar behavior for Zonshen. When Zonshen had the cure really for Sonic, Yilin and Chun warned Sonic of Zonshen's cures, where Yilin remarked that they tasted very, very bitter. She was confused, however, when she heard Chun claiming not to like them, as he ate everything. As Chun remarked that she made a fuss about Zonshen's medicines as well, Yilin rebuked that she drank them at least. After Sonic had drunk the medicine, which turned out not to work, Yilin and Chun asked him if it tasted bitter, which Yilin bet it did.
The following night, Zonshen tried to cure Sonic with pressure point techniques, but Yilin and Chun warned Sonic when they met him that these treatments hurt, to which Yilin replied that just thinking about them made her hurt. As Zonshen’s pressure point techniques failed to cure Sonic, however, Yilin and Chun asked Sonic if it hurt. Yilin was then amazed to hear that Sonic did not feel any pain, and called him a manly man and cool for that.
After that, Zonshen prepared to use his Zonshen Qigong technique to cure Sonic. Yilin and Chun later both saw Zonshen preparing the technique and they warned Sonic when they met him that their grandfather was preparing for a "big bang". However, both Yilin and Chun became worried about Zonshen as he became so wrapped up in his cure that he forgot to take care of himself. Yilin and Chun later met up with Sonic to explain the situation, where Yilin told about Zonshen's behavior. Chun then had the idea of give Zonshen his favorite snack to make him feel better, and Sonic headed out to get some. When Sonic later returned with the snacks, Chun thought about eating them himself, but Yilin stopped him. As Chun left to give the snacks to Zonshen, Yilin thanked Sonic for his help and told him that she thought that her grandfather would perk up if he had a drink old people liked. After Zonshen was back to normal and had treated Sonic, Yilin heard from Sonic that Zonshen's technique did not cure him, but tried to comfort him by telling him that she still liked him.
Some time later, Yilin and Chun met Charles from Empire City who had come to learn about Zonshen's treatment techniques, but they did not want Charles to meet Zonshen yet, so they held Charles back. When Sonic and Chip later returned to Chun-nan, Yilin asked Sonic if he knew Charles and if he was a friend of him. Deciding that Charles would not get to see Zonshen before they had some fun with him, Yilin and Chun decided to have Charles complete some tasks for them before they let him through.
The next day after Chun had had fun with Charles, it was Yilin's turn. As Charles asked her to see Zonshen, Yilin told him that he could not and told him to play hide-and-seek with her, claiming that Zonshen had said that he had to play with her before he got to see him before ran off to hide. Though Charles had Sonic do most of the work, Yilin thanked Charles for the game and took Charles to Zonshen. After Yilin had brought Charles to Zonshen, Yilin told Sonic and Chip that she had a lot of fun playing with Charles and that she thought he was a really nice guy.
After Charles met Zonshen, Yilin and Chun watched on as Charles continued to argue with Zonshen about the tasks he had given him and Zonshen getting angry with Charles' behavior. When Yilin and Chun met Sonic and Chip after that and had explained what had happen, Yilin remarked that they each seemed angry and worried.
Later on, during Sonic and Chip's battle with Dark Gaia, Yilin witnessed the local Gaia Temple rise from the ground. Yilin later watched on in horror with the rest of his village, while she clung to Hualin, as Dark Gaia began to cast the world into darkness while maturing into Perfect Dark Gaia, but later rejoiced when the world returned to normal following Perfect Dark Gaia's defeat at the hands of Super Sonic and the Gaia Colossus.
Yilin never made any real appearance during the PS2/Wii version of Sonic Unleashed, and only appeared during the cutscenes. During Sonic the Hedgehog and Chip's battle with Dark Gaia, Yilin witnessed the local Gaia Temple rise from the ground. Yilin later watched on in horror with the rest of his village, while she clung to Hualin, as Dark Gaia began to cast the world into darkness while maturing into Perfect Dark Gaia, but later rejoiced when the world returned to normal following Perfect Dark Gaia's defeat at the hands of Super Sonic and the Gaia Colossus.
Yilin is very sweet and innocent of nature. She loves to play hide-and-seek so much that she will stay hidden for days at a time.