Also known as Zhulong (Illuminating Dragon) and Shokuin in Japanese, Zhu Yin is a Chinese light and weather dragon deity that lives on Mount Zhōng, one of Heaven's gates to the North, - it appears as a 300 mile long dragon, with an elderly human male face instead of a draconic one. The earliest legend of China attributes daybreak to Zhulong opening his eyes, and nightfall to Zhulong closing his eyes - its cold breath brought about the winter season, while its warm breath brought about summer. It lives at the foot of its mountain and did not have a need to eat, drink or rest. The rain and wind are at its beck and call, along with his illumination being so great, it even pierces the depths of the Underworld.
"A snake god that controls daylight and the weather. He has the face of a human, but his eyes are vertical. He lives in the mountains of northern China, wrapped around them with his crimson body. He does not eat, sleep or breathe. It is day when his eyes are open and night when they close. If he blows, it becomes winter, and if he inhales it becomes summer."
"A snake god that controls daylight and the weather. He has the face of a human, but his eyes are vertical. He lives in the mountains of northern China, wrapped around them with his crimson body. He does not eat, sleep, or breathe. It is day when his eyes are open and night when they closed. If he blows, it becomes winter, and if he inhales it becomes summer."
—Shin Megami Tensei IV Apocalypse compendium
Zhu Yin can teach Nanashi the Rakukaja, Fog Breath, Posumudi and Dekaja skills through his Demon Whisper. He benefits from learning Ice, Force and support skills. Despite Zhu Yin having a rather poor affinity for Physical attack skills, most of the points raised while it levels up will go to Strength and Luck.
Shokuin can be obtained by evolvingWong Long, who has a 12.5% of chance of mutating into him (otherwise, he'll turn into Dagda). After being obtained, Shokuin is added to the list of Personas in the Velvet Room and can be summoned by using 352 World Cards. This event is carried over to a New Game Plus.
Known as Shokuryuu, he appears as a boss in Fire Book. A demon of Niflheim, he would disguise himself as Sandalphon and take his place. Later he would turn Enoch into a statue with the aid of his disguised ally Amphiptere. He will face him again in Niflheim, where he challenges him in Suneefiyoru. As he dies he reveals that even if all life is extinguished in the eternal battle, the war between Light & Dark will continue. The resurrected Shokuryuu can be found on the Acheron River.