Ni? () or Kong?rikishi (?) are two wrathful and muscular guardians of the Buddha standing today at the entrance of many Buddhist temples in East Asian Buddhism in the form of frightening wrestler-like statues. They are dharmapala manifestations of the bodhisattva Vajrapi, the oldest and most powerful of the Mahayana Buddhist pantheon. According to Japanese tradition, they travelled with Gautama Buddha to protect him and there are references to this in the P?li Canon as well as the Ambaha Sutta. Within the generally pacifist tradition of Buddhism, stories of dharmapalas justified the use of physical force to protect cherished values and beliefs against evil. The Ni? are also seen as a manifestation of Mahasthamaprapta, the bodhisattva of power that flanks Amit?bha in Pure Land Buddhism and as Vajrasattva in Tibetan Buddhism.
Kong?rikishi are usually a pair of figures that stand under a separate temple entrance gate usually called Ni?mon () in Japan, h?ngh? èr jiàng (?) in China and Geumgangmun () in Korea. The right statue is called Misshaku Kong? (?) and has his mouth open, representing the vocalization of the first grapheme of Sanskrit Devan?gar? (?) which is pronounced "a". The left statue is called Naraen Kong? () and has his mouth closed, representing the vocalization of the last grapheme of Devan?gar? (? ) which is pronounced "" (). These two characters together (a-h/a-un) symbolize the birth and death of all things. (Men are supposedly born speaking the "a" sound with mouths open and die speaking an "" and mouths closed.) Similar to Alpha and Omega in Christianity, they signify "everything" or "all creation". The contraction of both is Aum (?), which is Sanskrit for The Absolute.
Misshaku Kong? (?), also called Agy? (, "a"-form, general term open-mouthed statues in aum pair), is a symbol of overt violence: he wields a vajra mallet "vajra-pi" (a diamond club, thunderbolt stick, or sun symbol) and bares his teeth. His mouth is depicted as being in the shape necessary to form the "ah" sound, leading to his alternate name, "Agy?". Misshaku Kong? is Miljeok geumgang in Korean, Mìj? j?ng?ng in Mandarin Chinese, and M?t tích kim cng in Vietnamese. It is equivalent to Guhyap?da vajra in Sanskrit.
Naraen Kong? (), also called Ungy? (, "um"-form, general term closed-mouthed statues in aum pair) in Japanese, is depicted either bare-handed or wielding a sword. He symbolizes latent strength, holding his mouth tightly shut. His mouth is rendered to form the sound "h" or "Un", leading to his alternate name "Ungy?". Naraen Kong? is Narayeon geumgang in Korean, Nàluóyán j?ng?ng in Mandarin Chinese, and Na la diên kim cng in Vietnamese.
A manifestation of Kong?rikishi that combines the Naraen and Misshaku Kong? into one figure is the Shukong?shin at T?dai-ji in Nara, Japan. Shukong?shin (?), literally "vajra-wielding spirit", is Sh?kong?shin or Shikkong?jin in Japanese, Jip geumgang sin in Korean, Zhí j?ng?ng shén in Mandarin Chinese, and Ch?p kim cang th?n in Vietnamese.
Kong?rikishi are a possible case of the transmission of the image of the Greek hero Heracles to East Asia along the Silk Road. Heracles was used in Greco-Buddhist art to represent Vajrapani, the protector of the Buddha, and his representation was then used in China and Japan to depict the protector gods of Buddhist temples. This transmission is part of the wider Greco-Buddhist syncretic phenomenon, where Buddhism interacted with the Hellenistic culture of Central Asia from the 4th century BC to the 4th century AD.
Nio Zen Buddhism was a practice advocated by the Zen monk Suzuki Sh?san (1579-1655), who advocated Nio Zen Buddhism over Nyorai Zen Buddhism. He recommended that practitioners should meditate on Nio and even adopt their fierce expressions and martial stances in order to cultivate power, strength and courage when dealing with adversity. Suzuki described Nio as follows: "The Ni? (Vajrapani) is a menacing God. He wields the kong?sho (vajra) and he can crush your enemies. Depend on him, pray to him that he will protect you as he protects the Buddha. He vibrates with energy and spiritual power which you can absorb from him in times of need."