Warning: the following article contains spoilers for My Hero Academia Chapter #331, "United States of America," by Kohei Horikoshi, Caleb Cook and John Hunt, available in English from Viz Media.
The fight between America's #1 Hero and Shigaraki (or All For One?) continues to intensify with each new chapter. Star And Stripe is still exhibiting what makes her quirk so incredible and it seems the reasons are virtually endless. In Chapter 331, Shigaraki has undergone a sudden transformation in which his hair grew much longer. He has finally figured out how Star's Quirk works and its limitations.
The particulars of how Star And Stripe's Quirk works is highly classified information strictly overseen by the American government, which makes sense considering how powerful it is. It's also much easier to activate if her targets don't know how it works and therefore don't know what to do in order to prevent a rule from being assigned to them. However, despite the details of the Quirk being kept tightly under wraps, her public hero work gives a rough idea of how it works.
Shigaraki deduced that there must be a limit to how much she can power up and strengthen her body. Otherwise, she would've been able to kill him by crushing his head with pure power. He is right about this since she absolutely intends to kill him during this fight, yet she's having trouble accomplishing that. Moreover, Shigaraki figured out why the rule Start And Stripe tried to assign to him had no effect: it's because she referred to him as Tomura Shigaraki, but it isn't clear to anyone who or what he is at this point. He isn't even sure himself whether he's Shigaraki, All For One or some fusion of both.
Furthermore, he realized that when Star And Stripe calls the name of a target with a sense of self, her understanding of the target's identity must align with the target's own. However, if the target doesn't have a sense of self, her one-sided understanding is enough to enforce a rule. One of Star And Stripe's comrades asked her what they should do now, since Shigaraki's regeneration undid their previous attacks. She stresses that Shigaraki is no longer just a local menace of Japan, he's a global threat and that must die now. That means using tactics that Japan lacks.
Star then leads their counterattack by assigning a rule to the air, forming it into her shape, but 1000 times bigger. The rule takes effect but, since it's still air, Shigaraki is unable to see it. Star uses the mass of air to punch Shigaraki, sending him flying at incredible speed, then claps her hands, attempting to bust him down to atoms. She commands her comrades to fire all their lasers at her and uses her Quirk to combine them into one enormous beam.
The result is essentially a giant lightsaber that Star drives into Shigaraki. Star's comrades believe he'll burn away to nothing from the nonstop blast of the laser, but Star notes that, if this could defeat him, Endeavor could've finished the job himself. Star receives contact from the commander, Agpar, who informs her that a weapons strike is imminent. He also tells her to prepare to surpass All Might, since even he couldn't put a proper end to this villain. Agpar's strike is revealed to be an incoming bombardment of state-of-the-art hypersonic intercontinental cruise missiles known as Tiamat.
