WARNING: The following contains spoilers for Solo Leveling Chapter 164 by Chugong, Dubu and h-goon, available in English now on Tapas.
Solo Leveling's Jinwoo is about as OP a hero as you can get, but it turns out that this wasn't even his final form. At the beginning of the webtoon, Jinwoo was an E-ranked hunter who was constantly on the verge of death, only managing to survive by the skin of his teeth every single time. However, the Double Dungeon nearly did him in, and it was only because he was selected to be a Player by a mysterious program called the System that he survived.
The System put him through a strenuous training regime, turning him from a lanky young man into the strongest Hunter in the world while also inadvertently changing his appearance. Not only did the System train him, but it also allowed him to gain magical powers such as being able to heal himself. Jinwoo's strength seemingly had no limits -- but it turns out that the System had imposed some limitations.
After getting stabbed by the Beast Monarch in Chapter 161, Jinwoo is sent into an alternate dimension where time is reversed and he lands back in the hospital after his first Double Dungeon. As he goes through the motions of moving through his past again, messages constantly pop up from the System, asking him if he wants to "restart the world," implying that Jinwoo could start fresh if he wanted. Jinwoo confronts the Shadow Monarch, Ashborn, who reveals to him that he has been watching Jinwoo from the beginning.
Monarchs and Rulers need to have human vessels in order to descend to Earth, and while most of them have found a vessel, the Shadow Monarch was much too powerful for a normal human being to handle. Things get more complicated when said human being also has to withstand the powers of the King of the Dead. That's where the Architect came in. The Architect promised Ashborn to find someone strong enough to become his vessel as long as he could be granted immortality.
When Jinwoo was dying in the Double Dungeon and was chosen as the Player, it wasn't done by the Architect. Instead, the Shadow Monarch stepped in and overruled the Architect because he saw something in Jinwoo's raw desperation and desire to live, despite how close he was to death. To the King of the Dead, it made perfect sense for Jinwoo to become his vessel.
Even though Ashborn chose him, it didn't mean Jinwoo was ready. He was still much too weak to even win a fight in a Dungeon, which was why the System was designed in such a way to prime Jinwoo's body into becoming the ultimate host. Slowly, Jinwoo got stronger and began 'borrowing' some of the powers of the Shadow Monarch such as shadow extraction and shadow exchange. Despite being able to level up past Level 100, Jinwoo's powers were still capped.
The Architect had intended for Jinwoo to become just strong enough to withstand Ashborn's powers so that Ashborn could properly descend to Earth, but after everything he had been through -- the war and the Monarchs' betrayal -- the Shadow Monarch decided to save Jinwoo again. Instead of coming down himself, Jinwoo would inherit all of his powers and become his heir. Over the short period of time they spent together, Ashborn had grown fond of him, watching as he failed but always coming back stronger. There were a few moments in the webtoon when it looked like Jinwoo was becoming more detached from his humanity, but his fierce determination to protect his family became the foundation of his desire to protect the rest of the world.
Ashborn and Jinwoo were one and the same -- and frankly, after being on both sides of the same endless war, Ashborn was exhausted. He didn't want to keep fighting anymore, so his abilities weren't the only thing he gave Jinwoo; he also gave him the choice to choose the side to fight for.
Jinwoo's revival not only restored his powers but also broke the System. All of his shadow soldiers came back, powers restored, and in Igris's case, can now talk. Jinwoo was already badass enough, defeating countless Dungeon bosses, but little did audiences know that he wasn't even at his peak. The new Shadow Monarch has arrived, and there is now nothing holding him back.
