Gakusanjin

was a rock yōkai in the form of a mountain. He was in possession of the Fuyōheki that concealed his energy and let him sleep eternally.

History
Gakusanjin had been asleep for 200 years until Naraku entered his body. He stole the Fuyōheki from Gakusanjin to conceal his heart. This awoke Gakusanjin and asked who disturbed his slumber. He began to move away from his resting spot. This caused the parasites that used his body as a nest to run rampant in the area and possess other yōkai.

When Inuyasha and his friends heard rumors of a mountain that suddenly disappeared seven days ago. Inuyasha able to pick Gakusanjin's scent (as well as a faint trace of Naraku's). He followed it until they came across the giant yōkai. Gakusanjin suddenly tried to attack them, but they dodge it. Inuyasha angrily asked him why he attacked and of he was working for Naraku. Gakusanjin becme furious when he heard Naraku's name. He exclaimed that Naraku disturbed his slumber after inhaling his yōki and shōki when he entered his body. He then explained that Naraku stole his protective stone from within his body and escaped. He asked Inuyasha where Naraku was and said they he would not spare them if they were hiding him. He then proceeded to attack Inuyasha again. Inuyasha tried to explain that he didn't know where Naraku was and they he was looking for him to, but Gakusanjin wouldn't listen and said they his anger would not subside if he wasn't told of Naraku's location. Miroku suddenly asked Gakusanjin to tell more about his protective stone. Gankusanjin told him that the stone was essential for him to sleep while maintaining his existence as a mountain and called the stone the Fuyōheki. He explained that it dissipated his yōki and made it so he would not have to take part in unnecessary battles.

Inuyasha asked Gakusanjin to describe what the Fuyōheki looked like to him. Gakusanjin asked Inuyasha why he wished to know. He claimed that he would find it and return it to him, but Gakusanjin did not trust him and continued his attack. He was able to repel Gakusanjin with his Kaze no Kizu. Inuyasha told the others they should go since they would learn nothing from Gakusanjin. Gakusanjin was surprised and asked Inuyasha why he didn't kill him when he had the chance. Inuyasha took that as a challenge and was prepared to draw Tessaiga again. Miroku explained to Gakusanjin that their only enemy was Naraku and that fighting him would serve no purpose. He promised that they would return the Fuyōheki to him if they found it. Gakusanjin suddenly raised his left arm. Inuyasha thought that he wanted to continue fight, but he saw a bunch of crystals fall from his arm. Gakusanjin told them to take some of them and explained that they were his crystallized yōki. He told them that if they get close to the Fuyōheki, the aura from the crystals would disappear. Miroku and Sango stated that they earned Gakusanjin's trust and Kagome thanked him. Gakusanjin simply said enough and for them to go now. Kagura had listened in to their conversation and began to understand Naraku's objective. She grabbed one of Gakusanjin's yōki crystals after everyone had left they area.

Gakusanjin was later killed by the Gyōja because of their inability to make a distinction between evil yōkai and innocuous ones. The corpse of Gakusanjin was discovered by the group of Inuyasha. Afterwards it turned out that Goryōmaru deposited Gakusanjin's carcass in a cave to create a strong concentration of demonic aura.

Personality
Gakusanjin does not want to take part in unnecessary fights and desires to only be left alone to sleep. When he is awake, he is shown to be easily angered. He has grown a strong resentment towards Naraku for stealing the Fuyōheki from him and disturbing his sleep.

Powers & Abilities

 * Enhanced Strength: Gakusanjin is shown to be very powerful due to his size. His fists are strong enough to rupture the ground when he punches it.
 * Crystallized Yōki: Gakusanjin is able crystallize his yōki and separate it from his body. He does this to give Inuyasha and his friends a way of tracking the Fuyōheki.

Manga vs. Anime

 * In the manga, after Gakusanjin states that he can't trust Inuyasha and his friends when they claim that they will return the Fuyōheki to him, he acknowledges that they don't know where Naraku is and calls Inuyasha an eyesore before attacking him again.

Media appearances
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Manga

 * Chapter 335
 * Chapter 336
 * Chapter 346
 * Chapter 347
 * Chapter 348
 * Chapter 351

Anime
}} Gakusanjin Gakusanjin 岳山人
 * Episode 164 voice only
 * Episode 165
 * Episode 166