How ‘The Boys’ Turned Kimiko Into a Living Nuclear Reactor to Finally Stop Homelander

Few moments in the final season of ‘The Boys’ carry as much weight as the revelation that Karen Fukuhara’s Kimiko Miyashiro has been quietly transformed into the most important weapon against Homelander. It is a story arc that connects threads stretching back to Season 3, and it pays off in the most devastating and spectacular way imaginable in the series finale.

The journey to understanding how Kimiko acquired a version of Soldier Boy’s signature power requires unpacking the science, the sacrifice, and the desperate calculus of a group of people with almost nothing left to lose. What the show delivers is not a simple power transfer but a brutal, grief-soaked experiment that redefines what Kimiko means to the story of ‘The Boys’ entirely.

Soldier Boy’s Power-Erasing Blast and Why It Mattered

Soldier Boy developed the ability to discharge immensely powerful blasts of radiation-infused energy from his upper torso after gaining the properties of a living nuclear reactor. This was not a gift he was born with. The Soviets exposed him to massive, atomic bomb amounts of radiation, which turned him into a biological nuclear reactor. It is a gruesome origin story that the show planted as a narrative seed long before Season 5 decided to water it.

The blast nullifies the powers of super people, burning Compound V out of a supe’s system. Showrunner Eric Kripke told Variety that the goal was always to make Soldier Boy an existential threat to Homelander, since “the scariest thing in the whole world to Homelander is just to be a regular dude.” In cases such as Kimiko, Queen Maeve, and other Herogasm survivors, this resulted in full depowering and reversion to a normal human state.

When The Boys set Soldier Boy loose in Season 3, Kimiko bravely absorbed the onslaught and found herself knocked clean through a wall, and whereas regeneration would typically heal her wounds, she just kept losing blood from the impact. Losing her powers was initially something Kimiko quietly welcomed, having never chosen them. But the threat of the series finale made it clear that same destructive energy would need to exist somewhere else entirely.

Kimiko’s Radiation Experiment: Recreating the Soviet Formula

According to documents procured by the team, Soldier Boy got his power-erasing abilities after a decade of being exposed to radiation treatment. With that intelligence in hand, Butcher devised a plan to replicate the process on Kimiko, whose Compound V-enhanced biology gave her a fighting chance of surviving what would kill an ordinary human. With Butcher having studied tapes of the experiments on Soldier Boy, the plan was to blast Kimiko with radiation until she developed the same ability to remove a supe’s powers.

Frenchie and Kimiko ran test trials within a uranium radiation chamber, with Frenchie gradually exposing Kimiko to uranium radiation over time, hoping it would allow her to develop the same radiation blast ability Soldier Boy has. The process was agonizing and relentless. After each trial, it took Kimiko longer to heal over each interval, as mentioned by Frenchie. While she endured the radiation better than ordinary humans, her body showed only signs of internal damage and delayed recovery.

Frenchie kept exposing Kimiko to dangerous amounts of radiation, and after Sister Sage did the calculations three times, they found the exact level and exposure needed to recreate what the Russians had done to Soldier Boy. The involvement of Sister Sage proved crucial, since the precision required to compress decades of Soviet experimentation into a matter of days demanded her extraordinary intellect. Kimiko was locked in a chamber and exposed to extreme radiation for 30 seconds, her skin started to burn, and she fainted inside the chamber.

Frenchie’s Sacrifice and the True Cost of the Plan

Homelander arrived on the scene at the very end of Episode 7, as he was on the hunt for Sister Sage after she completely turned against him. With Kimiko weakened from the final test run and Homelander bearing down on their hideout, Frenchie made a choice that changed everything. With limited options, Frenchie stepped inside the chamber they were using for Kimiko’s radiation experiments.

Frenchie informed Homelander that the radiation treatment was ready and that the team was coming for him, then pulled the switch and exposed both himself and Homelander to the radiation. It was an act of both defiance and self-destruction. Once Homelander confronted him inside, the OG Boys member activated the powers, exposing both himself and Homelander to the radiation, despite knowing it would kill him. Frenchie was bleeding out after Homelander departed, allowing him to have one final moment in Kimiko’s arms.

After seven years, Frenchie became the first core member of ‘The Boys’ to die, lasting all the way until the show’s penultimate episode before his tragic demise. His death did not just serve as an emotional gut-punch. It functioned as the ignition for Kimiko’s transformation from test subject to weapon. With Kimiko the one given new powers and set up as the hope to defeat Homelander, there has to be a tradeoff, and victory always comes at a price in this show.

How Kimiko’s New Ability Brought Down Homelander in the Finale

Frenchie, just before his death, managed to give Kimiko that same ability that was given to Soldier Boy through torturous doses of radiation. In the series finale, that power became the linchpin of the entire endgame against a Homelander who had received a dose of V1, granting him near-immortality. The plan required more than just the blast itself; it required holding the most dangerous supe alive long enough for Kimiko to deploy it.

Ryan and Butcher managed to subdue Homelander long enough for Kimiko to use her nascent nuclear bomb-style superpower on him. That ability was one she acquired after Sister Sage and the recently deceased Frenchie successfully recreated the experiment that gave Soldier Boy a similar superhuman trait.

The blast was not surgical. The resulting blast not only hit Homelander, Butcher, and Ryan, but stripped the supe-creating Compound V serum from their bodies, thereby permanently depowering them all.

In perhaps the most cathartic moment of the series, Butcher beats Homelander to a bloody pulp, who cries and begs for his life until a crowbar is driven through his skull. Homelander is finally defeated and killed once and for all. It is a conclusion that gives Kimiko’s entire arc across five seasons a brutal and earned resolution. The woman who had powers forced upon her as a child, who lost them and chose to reclaim them for love, ultimately weaponized her own suffering to end the worst monster the show ever produced.

For a series built on the idea that power corrupts, it feels right that the person who brought Homelander down was never chasing glory to begin with, and if you have thoughts on whether Kimiko’s arc landed the way it deserved after everything Frenchie sacrificed to make it happen, this is the moment to share them.