Yotsuyu Yagiyama

Yotsuyu Yagiyama (八木山夜露) is an antagonist appearing in Part VIII: JoJolion.

Yotsuyu is the architect of the Higashikata Family mansion, Fruit Parlor and the Baseball stadium where Aishou Dainejiyama works. He is acquainted with and is responsible for killing Josuke's complete former identity, Josefumi Kujo.

Appearance
Yagiyama is a man of slim build and average to above-average height, claiming to be 28 years old. He has shoulder-length, straight black hair with short bangs. His eyes are black with a small triangular highlight.

He wears a headpiece of leaves and a collar with a pin bearing the letter H. His arms and legs are clad in a dark, leathery material studded with small metallic spikes.

Later, his sex comes into question when his corpse is discovered to lack male external genital organs.

Personality
Cruel and calculating, Yotsuyu states that above all he desires social status. He demonstrates manipulative prowess when exploiting Tsurugi's fear of his family's disease to coerce him into assisting in trapping Josuke. As Josuke states Yotsuyu is the type of person who will attack innocent people in order to show he is serious about his threats.

Apparently, he has some previous encounter with the man who fused with Yoshikage Kira. He expresses annoyance at how persistent of a hindrance Josuke is after exclaiming that he returned to life even after Yotsuyu himself killed him.

Despite all of that Aishou recalls Yagiyama in a positive and helpful light as note in his flashback where Yagiyama appeared to be sympathetic and supportive of the more naive Aishou after he finds out his girlfriend has betrayed him.

Like all Rock Humans shown thus far he has an interest in the Rokakaka Tree and it's fruit, to the point where he is willing to eliminate anyone else who might have information that could hinder his motives.

Stand
Yotsuyu's Stand is I Am a Rock; able to attribute a force to targets attracting to one type of object at a time. Additionally he is able to attract rocks to himself to cause damage to people or objects close to him, but it is unclear if he can use this to attract other objects.

Rock Physiology
While similar to a human's, Yotsuyu's body can change into rock. Because of this, he does not need to sleep or rest. He can mimic rocks to the point that he is indistinguishable from them.

Norisuke theorizes that Yotsuyu's physiology requires him to have at least a small amount of skin respiration and in the absence of such his body structure will begin to break down due to it becoming less structurally stable than an ordinary human's.

Also it is curious to mention that Yotsuyu was able to produce a strange transparent film from his eyes/mouth which he used to waterboard Yasuho but at this stage it isn't confirmed whether this is a trait all 'Rock Humans' possess or something exclusive to Yagiyama.

Synopsis
According to Aishou's flashback at some point before the events of JoJolion, Yotsuyu was there to inform Dainenjiyama of his girlfriend's betrayal and it is implied that the two were at least acquainted with one another beforehand. He also mentions to have been the one to kill Josuke's original self by 'crushing him between two rocks' and remarks that if not for Kira Josuke would never have been revived. Yotsuyu Yagiyama first mysteriously appears in the story within the secret room below the Higashikata estate, watching Yasuho Hirose sleep. He uses his Stand power to suffocate her in an attempt to draw out Paisley Park and examine it. Once Paisley Park manifests, he uses his Stand to trap it in place, and seems to be able to identify its unique abilities, such as it being a long-distance type Stand. While she is still trapped, he reveals that he is an architect scouting out interesting properties, such as the secret room, and states that he hopes that Josuke never retrieves his memories, appearing to know more than he lets on. Yasuho, in a last ditch attempt to free herself, manages to fold an origami bunch of bananas, which she successfully uses to trip Yagiyama, as they are still powered by Tsurugi Higashikata's Stand Paper Moon King. Yagiyama falls onto broken glass Yasuho had earlier tried to use to cut the film on her face, and in the confusion his Stand's power weakens, freeing Yasuho from the film. Though seemingly injured, he mysteriously disappeared.

Later, he assaults Josuke and Norisuke as they attempt to gain access to the basement by touching Josuke's foot and activating his Stand to cause large flower pots to accelerate towards them as he watches from the entrance, surprised Josuke would return to the location just to die again. When the two manage to avoid the flower pot shards piercing into their bodies he activates his Stand a second time, only to cause thousands of chestnuts to advance on them instead. When this fails Yotsuyu resorts to kidnapping Yasuho from inside the basement cellar and takes her out through the hidden fault in the roof caused by the earthquake. Josuke and Norisuke follow him using the latter's Stand King Nothing to track Yasuho's scent. He lays her down among rocks close to the shoreline and proceeds to hide so that when the two approach he can catch them by surprise using his rock skin to blend into his surroundings. This ambush culminates in him using his Stand for a third time; in order to lure Josuke outside and engage in a final ploy by attracting Dozens of Pesticide containers to him, hoping that they would burst and the liquid would seep into his skin and poison him. Josuke's response is to encase Yotsuyu in a large soap bubble, intending to carry him off and drop him into the sea but Yagiyama is able to attrack several nearby rocks towards himself in order to pop the bubble and set himself free, thinking he had foiled Josuke's plan. In reality Josuke was merely positioning Yotuyu closer to the shore so that he could tackle him off of the cliff-side into the water below.

In the end, Josuke used his soap bubbles to push Yotsuyu into the sea in an attempt to force information out of him, preventing them both from surfacing by wrapping his body in nets Norisuke salvaged from the shoreline. However the unexpected happens when Yotsuyu's rock human physiology causes his body to break down when he no longer is capable of skin respiration and Josuke unintentionally kills him. As his body breaks apart, Josuke spots the mysterious fruit floating away from his pocket and disappearing into the ocean current.

Trivia

 * Yotsuyu's unique rock physiology and Norisuke's inferences at how he could be another species altogether mirrors the characteristics of the Pillar Men from Part II: Battle Tendency. Josuke had even intended to trap him permanently underwater like Magenta Magenta before him, in the same way Kars was blasted into space.
 * He shares the the same occupation as an architect with Masazo Kinoto.
 * Like Aishou Dainenjiyama, Yotsuyu's surname is a reference to sets of mountains in the Sendai region, which is the real world location of Morioh and the home city of Hirohiko Araki.