Longnü (traditional Chinese: 龍女; simplified Chinese: 龙女; pinyin: Lóngnǚ; Sanskrit: nāgakanyā; Vietnamese: Long nữ), translated as Dragon Girl, along with Sudhana are considered acolytes of the bodhisattva Guanyin (Avalokiteśvara) in Chinese Buddhism. Her presence in Guanyin's iconography was influenced by tantric sutras celebrating the esoteric Amoghapāśa and Thousand-armed forms of Guanyin, which mention Longnü offering Guanyin a priceless pearl in gratitude for the latter visiting the Dragon King's palace at the bottom of the ocean to teach the inhabitants her salvific dharani.

There are no scriptural sources connecting both Sudhana and Longnü to Avalokiteśvara at the same time. It has been suggested that the acolytes are representations of the two major Mahāyāna texts, the Lotus Sūtra and the Avataṃsaka Sūtra, in which Longnü and Sudhana appear, respectively.

The depiction of Longnü and Sudhana with Avalokiteśvara may have been influenced by Yunü (Jade Maiden) and Jintong (Golden Youth) who both appear in the iconography of the Jade Emperor. She is described as being the eight-year-old daughter of the Dragon King (traditional Chinese: 龍王; simplified Chinese: 龙王; pinyin: Lóng Wáng; Sanskrit: nāgarāja) of the East Sea.

Longnü is depicted in the 12th Chapter of the Lotus Sūtra (Skt. Saddharma Puṇḍarīka Sūtra) as being full of wisdom and achieving instant enlightenment. In the Lotus Sūtra, Mañjuśrī Bodhisattva speaks of her, saying:

There is the daughter of the nāga king Sāgara who is only eight years old. She is wise; her faculties are sharp; and she also well knows all the faculties and deeds of sentient beings. She has attained the power of recollection. She preserves all the profound secret treasures of the Buddhas, enters deep in meditation, and is well capable of discerning all dharmas. She instantly produced the thought of enlightenment (Skt. bodhicitta) and has attained the stage of nonretrogression. She has unhindered eloquence and thinks of sentient beings with as much compassion as if they were her own children. Her virtues are perfect. Her thoughts and explanations are subtle and extensive, merciful, and compassionate. She has a harmonious mind and has attained enlightenment.

However, the Buddha's disciple Śāriputra, a Sravaka, does not believe that a woman can attain buddhahood. In response, the nāga maiden offers a pearl to the Buddha, symbolizing her life and ego, and he accepts it. She then instantly transforms into a perfected male bodhisattva, and then attains complete enlightenment. According to Schuster, the Lotus Sutra's argument "is directed against the notion that some bodies (male) are fit for the highest destinies, and other bodies (female) are not."

In Chan Buddhism, the story was taken as an example to emphasize the potential of sudden awakening.

A single chapter in the Complete Tale of Avalokiteśvara and the Southern Seas (Chinese: 南海觀音全傳; pinyin: Nánhǎi Guānyīn Quánzhuàn), a sixteenth century Ming dynasty novel is the first text that connects Longnü and Sudhana together as being acolytes of Avalokiteśvara. When the Eastern Sea Dragon King's third son was out for swim in the sea in the form of a carp, he was captured by a fisherman. Unable to transform into his dragon form due to being trapped on land, he was going to be sold and butchered at the local market. Once Avalokiteśvara learned of his predicament, she gave Shancai all her money and sent her disciple to buy him from the market and set him free. Because the carp was still alive hours after it was caught, this drew a large crowd and soon a bidding war started due to people believing that eating this fish would grant them immortality. Shancai(Red Boy) was easily outbid and begged the fish seller to spare the life of the fish, but to no avail and earning the scorn of the people at the market. It was then that Avalokiteśvara projected her voice from far away saying, "A life should definitely belong to one who tries to save it, not one who tries to take it". The crowd realizing their mistake soon dispersed and Shancai was able to bring the carp back to Avalokiteśvara and return it to the sea.