Warning: the following article contains spoilers for Jujutsu Kaisen Chapter 171 "Tokyo No. 1 Colony, Part 11" by Gege Akutami, John Werry, and Snir Aharon, available in English from Viz Media.
Fushiguro cleverly lured Reggie into a gymnasium in the previous chapter with a plan in mind. Reggie figured he was up to something but was clueless as to what. Moreover, he made the mistake of assuming that Fushiguro lacked big moves. Fushiguro activated his Domain Expansion, Chimera Shadow Garden, completely blindsiding Reggie once they were inside the gym.
Reggie quickly recovered from his shock in Chapter 171 and activated a form of the New Shadow Style: Simple Domain technique that hasn't been seen in the series before. Several characters have demonstrated the use of the typical Simple Domain technique. However, readers have never seen it used in this way before. This form of the Simple Domain also seems to be uncommon compared to the usual one since it's called an esoteric technique.
Hollow Wicker Basket was the original form of New Shadow Style: Simple Domain. It neutralizes a Domain to negate the guaranteed hit effect, just like the modern form of the technique. Domain Expansions are meant to grant the user guaranteed hits and neutralize their target's cursed technique. Simple Domain is a direct counter to this as the user will not be affected by the Cursed Technique imbued in the Domain or the guaranteed hit. The user of a Domain Expansion also becomes vulnerable to attacks when another Domain is cast within their own.
Reggie believed he was safe from Fushiguro's attacks but is surprised when he's hit with an attack. He missed the fact that Fushiguro's Chimera Shadow Garden was not a complete Domain. Fushiguro was not able to close the barrier of his Domain on his own, which is why he lured Reggie into a gymnasium and forcibly did so within that space. Since his Domain is incomplete, the barrier does not have the guaranteed hit effect. Chimera Shadow Garden was only extending Fushiguro's Ten Shadows Technique and expanding its potential to 120 percent.
Simple Domains, including Hollow Wicker Basket, are meant to neutralize Domain Expansions, not Cursed Techniques themselves. That works out perfectly for Fushiguro since he uses shadow clones and his shikigami with just his Cursed Technique. The reason they can hit Reggie despite his Simple Domain was that Fushiguro was not using his Domain to attack. He was simply using his Cursed Technique while his Domain was acting as an enhancer, making his hits more powerful. This made the incomplete Chimera Shadow Garden more dangerous than a guaranteed hit Domain.
Reggie realized this and acknowledged that it could result in him losing. This loss will most likely mean his death so he swiftly figured out a solution. He noticed that while Fushiguro is able to store things in his shadow, he's only been using one meager weapon. This struck him as odd because if the entire Domain is his shadow it would make sense that he'd have more weapons stored. He correctly deduced that Fushiguro must be forced to bear the weight of whatever he kept stored in his shadow. Meaning that his shadow was essentially like a big backpack and he feels the weight of anything he carries inside it.
Reggie used this to his advantage by manifesting three whole cars with his receipts and allowing them to sink into Fushiguro's shadow on the floor. This of course weighed Fushiguro down to the point of being unable to stand, but Reggie missed the fact that there's also shadow above him. After all, a Domain is still a Domain even if it's incomplete. Fushiguro released Max Elephant directly above Reggie and it falls on him. The two are now in a clash to see who'll be the first to get crushed by unbearable weight.
