Pharos Hercules

The main antagonist, a dream demon who leads a group of others to the real world so they can possess humans. His plan is to turn the real world into a place where dream demons can manifest without needing humans as vessels.

Appearance
Hercules looks like an armor, his skin is black with deck circle-shaped marks all over his body.

Personality
He is completely amoral, as he told Clione that he doesn't care about what happened to Landsborough or Chain Noir despite them being completely loyal subjects of his. When engaging in battle, he always shouts "It's showtime!".

History
John stated that he and Merry arrived in the real world at around the same time, almost a decade ago, but that his power hadn't started manifesting until very recently.

At some point, he possessed Takateru Akiyanagi. He also forced Clione to possess Taka's younger sister so Clione could track down dream demons in the real world, furthering his cause.

Some of his minions included Landsborough and Chain Noir, though Merry successfully sent both back to the dream world.

Hercules has come to the human world to attract the other nightmares. To then make them fight and use their powers to harm both sides of the door for all the nightmares are forced to manifest in the real world without a vessel.

Plot
He has the plan to eliminate the Gate that separates reality from the Dream World so that dream demons can roam Earth without the need for vessels.

He arrived on Earth a year ago, bringing Sonar Clione with him and they both wound up possessing the Akiyanagi siblings. John Doe assumed that when Hercules arrived with "a female" it was Merry. However, Merry is revealed to have already disappeared by the time he walked through the Gate. As a matter of fact, it was because Hercules discovered the vacant Gate that the dream demon invasion began in the first place.

Because his goal is to eliminate the Gate, he manipulated everyone in both worlds. He made dream demons come over from the dream World and fight each other in reality, making the shockwaves from those battles damage the Gate. He also made enemies of dream demons, slaying them so he could add their power to his "Memory Flame" technique.

Eventually, it is revealed that he and Yumeji are "brothers" because they "share the same blood" from the same source, explaining their similar abilities. Enji obtains Patty's sword thanks to Hercules's technique (which backfired on him) and Merry sends him back to the Dream World throiugh the Gate.

Hercules loses his power and appears before the Gate in front of a mysterious naked figure, the true antagonist who granted him his powers. With one drop of blood, the figure kills Hercules.

Powers & Abilities
He wields a scythe-like axe in battle, as when he fought Engi. He can also turn his left arm into a cannon to fire blasts of energy. He can also summon pillars of energy to erupt at any given location and can manifest and control powerful flames.

Hercules has the ability, like Yumeji, to use the Lucid Gadgets of other dream demons. He does so first by summoning Patty's sword to mock Enji, and later in battle when he summons Cactus's spikes to attack the group at once. He takes this ability further with a spell called "Memorial Flame" which he claims summons the memories of dream demons he's killed; it doesn't matter of the phantoms created are from his own memories, or another's. The phantoms manifested all have his pupils in place of their own, signifying his possession of them. This power comes from his Garden's "heart", the biggest tower that has a furnace with flames from the dreams demons he has slain.

He can also summon his own Garden at will in place of other dream demons, and seems to favor using his insignia (his pupils) whenever using his powers.

He still needs a vessel to manifest in the real world as he uses Takateru Akiyanagi to pull everyone into his Garden.

Most alarmingly, he has proven immune to Merry's power of sending dream demons back to the Dream World. Even when she entered "Gate Keeper" Mode out of grief caused by Yumeji's (believed) death, she was unable to significantly harm him in any way with the brunt of her full power. This could be because, with his Lucid Gadgets, he may actually be an amalgamation of dream demons. (Merry has shown she can only send one or two dream demons back at once).

Relationships
Takateru Akiyanagi: His human vessel. He has possessed Taka since the entire group was in elementary school, asking Yumeji not to look at his dream aura to avoid Yumeji discovering the truth of Taka's possession.

Sonar Clione: He forced her to possess Miyuki, Taka's sister, to locate dream demons in the real world.

Landsborough: Along with Chain Noir, he commands them into recruiting more dream demons to possess humans in the real world.

Yumeji Fujiwara: Yumeji is his elder brother. He tends to look down upon Yumeji yet at the same time, perceives him as a substantial threat to his plot. He also doesn't seem to feel any sense of familial attachment or compassion for Yumeji as he does not hesitate to kill him and even seems to derive sadistic amusement from physically beating him.

Trivia

 * "Pharos" (Φάρος) is the greek word for "lighthouse". Hercules' name is likely based on the island of Pharos, where the Lighthouse of Alexandria was built, and on the Tower of Hercules, a lighthouse located in north-western Spain.
 * It was revealed that Takateru Akiyanagi is his vessel.