Sung Jinwoo is widely recognized as one of the strongest anime characters in history. After Jinwoo became a Player, he gained several new abilities, one of which was Shadow Necromancy. If a person or creature died before him, Jinwoo could resurrect them as a Shadow Soldier.
Since then, he has used the ability many times and greatly increased the number of soldiers in his Shadow Army, but the ability does not have a 100% chance of success. Despite the contradictory assumptions, Jinwoo had amassed a lot of incredible fighters. Since Jinwoo's story is far from over, there are several other characters he could potentially recruit into his shadow army in the future.
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Go Gunhee was Korea's first S-rank hunter
Go Gunhee is the chairman of the Korean Hunter Association. He was Korea's first S-rank hunter, making him one of the strongest fighters in the series. Sadly, Go Gunhee is well past her prime in the current timeline, meaning she can't fight as freely as she used to.
However, Go Gunhee is still above the level of most Hunters, and that is because he is not an ordinary human. The truth is that he is a vessel for the Ruler, which gives him tons of power. Due to his old age, he cannot fight as freely, but if he were to become a soldier in Jinwoo's army, things would become quite interesting. Even if Go Gunhee would lose his abilities as a vessel, he would still have the potential to become stronger because Jinwoo's Shadows can level up.
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Thomas Andre was the nation's strongest hunter
Thomas Andre is one of the five national level hunters in the series and along with several others fought to take down Kamish, widely believed to be the strongest magical beast. After their victory, all five were worshiped around the world.
Thomas was the one who gained the most popularity of them all and established himself as the strongest hunter in the world. World Solo leveling he's cruel and merciless, so it wouldn't be surprising if Thomas Andre perished and joined Jinwoo's Shadow Army in future seasons. His addition in particular would take the protagonist's army to new heights.
4
Goto Ryuji stood above every Japanese hunter
Goto Ryuji was Japan's strongest hunter and was involved in the Jeju Island arc. He traveled to Korea to create a plan to destroy the ants on Jeju Island. Goto Ryuji was confident in his abilities and knew that the mission would be easy for a Hunter with his skills.
Little did he know that he would not leave Jeju Island alive. While Goto Ryuji was able to wipe out ordinary ants without much trouble, he was unable to do anything against the Ant King. He destroyed the Japanese hunter in the blink of an eye. Even though Sung Jinwoo didn't turn Goto Ryuji into a soldier, one can't help but think how valuable he would be to the Shadow Army.
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Yuri Orloff had the best barrier abilities
Yuri Orloff was the strongest S-rank Hunter from Russia. The Japan Hunters Association approached him and made him a very generous offer. As most of Japan's S-rank fighters were destroyed during the raid on Jeju Island, the government needed outside help to deal with the gate that was about to open in the country.
Yuri considered himself an expert on barriers and was sure that he could hold the gate with no problem. However, his illusion was shattered the moment he saw a giant emerge from the gate. Unfortunately, Orloff was killed by the giants, leaving the fate of the land in Jinwoo's hands. Jinwoo did save the country, but he never got around to awakening Yuri Orloff as a soldier.
Who is that character?

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Kamish was considered the greatest enemy of mankind
Kamish's arrival on Earth was one of the planet's greatest tragedies. The dangerous magical beast used its powers and mowed down one S-rank Hunter after another. Things looked bleak, but luckily Thomas Andre and his companions took matters into their own hands. After a grueling fight, Kamish was taken down.
Although the incident took place many years before Jinwoo's ascension, the hero was given the opportunity to encounter a deadly beast. He even managed to wake up Kamish, albeit temporarily. The author probably didn't want to overpower Jinwo too much by giving him Kamish.
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The architect created the system
The Architect or Kandiaru is the main antagonist in Solo levelingand it was the person who designed the System that granted Sung Jinwoo his powers. After Jinwoo reached level 100, the architect invited him to Cartenon Temple. He should have checked if Jinwoo had reached the required level.
The villain sent various statues to fight Jinwoo, and after the hero crushed them, the architect decided to enter the fray himself.
Jinwoo's fight against Kandiar was quite challenging and the hero was pushed to his limits. However, he was able to persevere through sheer force of will. Jinwoo defeated the architect but did not use his necromancy on him.