WARNING: The following contains spoilers for Season 1, Episode 2 of Tower of God, "Three Four-Hundredths," streaming now on Crunchyroll.

Shinsu is the strange, water-like substance introduced in the second episode of Tower of God. According to Lero-Ro, a Test Administrator who has reached the Tower’s highest floor, Shinsu is the air people breathe inside the Tower, but it can also be controlled and transformed by those who know how to use it. The higher one ascends through the Inner Tower, the heavier the Tower’s Shinsu becomes until it crushes anyone who cannot resist its weight.

Lero-Ro then displays how Shinsu works on the Tower’s upper floors by creating a wall of high-pressure Shinsu and forcing the Regulars to push their way through it. Many of the Regulars strain and struggle to pass the wall, and some of them are not able to pass through at all. Even among those who effortlessly slip through, only one person is completely unaffected by Lero-Ro’s Shinsu wall -- Bam, the one who came from outside the Tower.

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Shinsu takes many forms inside the Tower, but it can be best understood as a fusion of magic and air. In terms of being magic-like, Lero-Ro explains that Shinsu can be turned into fire, light or just about any element by those skilled enough. Those with less control can use it to strengthen their bodies or use other useful abilities in combat. It can even be used to craft weapons, as we saw in the case of the Black March. In fact, almost anything supernatural or magical inside the Tower can be explained by or traced back to Shinsu.

Though it can be controlled, Shinsu is primarily a natural substance. In high concentrations, Shinsu has water-like properties, but it is usually invisible and serves as air inside the Tower. Everyone breathes Shinsu inside the Tower, including its animal and plant life. In fact, even the blue sky seen on the ceiling of the Tower’s second floor is simply a reflection of the floor’s Shinsu -- it’s completely artificial. Shinsu is the foundation of all life inside the Tower. Within the Inner Tower, Shinsu becomes thicker and heavier the higher one climbs, forcing anyone who wants to climb the Tower to have a naturally high Shinsu resistance.

In fact, Bam has already had a taste of the higher floors’ Shinsu levels. During Headon’s test, Bam walked through a massive cage and faced an enormous, floating White Steel Eel. The space inside the cell is strangely green, and Bam breathes heavily while taking slow, careful steps. This cage actually contained a very high concentration of Shinsu, which was so thick that it allowed the creature inside to swim around in it. A normal Regular may have fallen from simply entering the cage, but Bam was able to cross through it.

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Naturally, most Rankers -- people like Yuri and Evan who have been to the top of the Tower -- are able to control and resist incredible amounts of Shinsu. Lero-Ro demonstrates this when he creates the Shinsu wall and later when he attacks an upset Regular with an even higher concentration of Shinsu. However, a side effect of living inside of high densities of Shinsu found inside the upper floors is that it slows how quickly you age. In fact, many Rankers are hundreds of years old, if not thousands. Many of those years were likely spent just trying to reach the top of the Tower, which attests to the sacrifices, difficulties and unwavering will required to reach that goal.

However, of all the people who interact with Shinsu in their daily lives, one enigmatic group has a notably distinct relationship with it -- the Irregulars. Bam is the only Irregular we’ve seen inside the Tower so far, but he has already displayed an impressive amount of Shinsu resistance during his tests with Headon and Lero-Ro. Although Yuri and Evan claimed that Bam is incredibly weak for an Irregular, his resistance was still high enough for Lero-Ro, an accomplished Ranker, to consider that Bam was a monster.

Shinsu is a substance that is as dangerous as it is mysterious. It pervades every inch of space within the Tower, giving life to its inhabitants and granting some of them strange abilities. It can be controlled and withstood, but that also comes with side effects, such as no longer being able to age. Despite coming from outside the Tower, where Shinsu doesn’t exist, Irregulars such as Bam can naturally resist it. While Bam has only experienced two encounters that utilized Shinsu, this may be only the tip of the iceberg for what his status as an Irregular will bring.

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