WARNING: The following contains spoilers for Jujutsu Kaisen Chapter 149, by Gege Akutami, John Werry and Snir Aharon, available now in English from Viz Media.
Chapter 149 of the Jujutsu Kaisen manga sees Maki get a significant power-up. Through the death of her twin sister and completion of her Heavenly Restriction, Maki has now obtained unrivaled speed and strength. But why did this happen, and how does Heavenly Restriction work?
Heavenly Restriction is a binding on the body that a sorcerer is born with, in exchange for power in another areas. Kokichi Muta, aka Mechamaru, was born with a useless right arm and legs, no feeling below the waist, skin so sensitive it can't stand moonlight, and chronic pain described as needles poking every pore. As a result, he can use his cursed technique, Puppet Manipulation, with a range as extensive as the country of Japan -- which would be impossible for the average jujutsu sorcerer. However, more mysteries remain.
One detail of Heavenly Restriction that remains unclear is whether the increase in power is negated if the restriction is removed. In Chapter 70 of Jujutsu Kaisen, Mechamaru’s body was healed by Mahito via his cursed technique, Idle Transfiguration. Shortly after, a battle ensued in which Mechamaru used cursed energy that he'd been storing over the past 17 years. As the fight progressed, the stored energy began to rapidly deteriorate. This may imply that the increase in cursed energy due to Heavenly Restriction had returned to normal levels after being healed.
Chapter 149 showcases another example of Heavenly Restriction changing over time when Maki is given a massive increase in strength. Originally, her Heavenly Restriction increased her natural physical prowess in exchange for lowering her cursed energy levels to that of a civilian. While Maki's physical capabilities put her on par with the average sorcerer, she had no ability to manipulate cursed energy, no cursed technique, and even required special glasses to perceive curses.
However, during Maki and Mai’s battle with their father, Ogi Zenin, more information is revealed about the twins’ abilities. While Maki was affected by Heavenly Restriction, Mai was given the cursed technique creation. According to Mai, cursed techniques treat twin children as one being, thereby diluting its effect between the twins. As a result, Maki’s Heavenly Restriction and Mai’s cursed technique/energy affected them both. Following Mai’s death during the battle, Maki’s Heavenly Restriction became fully realized. This gave her strength rivaling Toji Fushiguro, who is also affected by Heavenly Restriction.
Like Maki, Toji was a descendant of the Zenin clan and born without any cursed energy -- even the low levels a civilian gives off -- in exchange for monstrous physical prowess and the ability to perceive curses without the need for cursed energy. During Jujutsu Kaisen's “Gojo’s Past” arc, Toji is shown to be strong enough to go toe-to-toe with Satoru Gojo and Suguru Geto, two of the four sorcerers to be named special grade.
In the “Shibuya Incident” arc, Toji's body actually overwrites the technique, body and mind of another sorcerer who had attempted to steal his own body and utilize his physical abilities. After fully possessing his opponent, Toji went on to invade the domain of the special grade who was facing off against Nanami, Megumi Fushiguro, Maki, and Naobito Zenin, and quickly killed the curse. In contrast, the combined forces of the other sorcerers were succumbing to its strength.
As evidenced by its uses in Jujutsu Kaisen thus far, Heavenly Restriction is a powerful yet costly technique.