Fugen Shinjin is a prominent sennin, or immortal, from the anime Soul Hunter. He holds the position of the newly appointed leader of the twelve Kongrong Mountain Juunisen, the most powerful sennin of Kongrong, taking over after another member's departure. At the age of seventy-two, he shares the same age as his best friend and sworn soul brother, Taikoubou, with whom he trained. This deep bond is illustrated by the gift of a straight fishhook he gave to Taikoubou. Because sennin are not permitted to eat meat, and knowing his friend only fishes for quiet contemplation rather than to cause harm, Fugen provided the hook so that no fish would suffer needlessly. The two share a profound mutual regard; Taikoubou considers Fugen someone he absolutely cannot allow to die, while Fugen views Taikoubou as the sole reason for his own existence.

In terms of personality, Fugen is characterized as one of the most peace-loving sennin. He possesses a kind, compassionate, and almost angelic demeanor, often maintaining a gentle smile even in dire situations. This pacifistic nature directly informs his personal philosophy and his approach to combat. He strictly adheres to the belief that if negotiation fails three times, then it becomes impossible to resolve a conflict peacefully. True to this code, his fighting style involves defending himself without retaliating while attempting to persuade his opponent to cease fighting. However, should his third attempt at negotiation be rejected, he will not hesitate to strike down his adversary with full force.

His role in the story is defined by his position as a leader among the sennin and his unwavering loyalty to Taikoubou. He is also responsible for his pupil, Mokutaku, who is one of the character Nataku's two brothers.

Fugen's notable abilities are centered around his paopei, a mystical treasure, known as the globe-shaped Taikyokufuin. This weapon possesses the phenomenal power to manipulate atoms at a molecular level, capable of breaking chemical bonds or creating new ones. The true versatility of this power comes from Fugen's extensive knowledge of physics and chemistry, which enables him to wield the entire periodic table as a weapon. Beyond its offensive capabilities, the Taikyokufuin can function as a radar and has pre-programmed instructions that activate if Fugen is ever separated from it. His development within the narrative ultimately leads to his death during the Great Sennin War.