Godzilla[]
Serizawa, Graham, and a team of Monarch scientists observe the male MUTO while it is cocooned and feeding on the plant's reactor 15 years after the 1999 Janjira power plant catastrophe. After being notified by Vivienne of a new rise in the cocoon's activity, Serizawa travels to the plant via plane. Serizawa and Graham are hauled onboard the USS Saratoga after the MUTO breaks free from its cocoon and destroys Monarch's research center. They will assist the US military, led by Admiral William Stenz, in hunting down and destroying the MUTO.
Serizawa believes that Godzilla has risen to kill the MUTO, his kind's natural nemesis, after discovering his reappearance. When Godzilla swims beneath the Saratoga and meets the MUTO in Honolulu, Serizawa is proven true. Serizawa begins investigating the MUTO's echolocation signals more closely after both Godzilla and the MUTO have left Honolulu. According to Serizawa, the MUTO was interacting with a female — the dormant spore — which had been transported to a nuclear waste storage in Nevada at the time. A team of troops is dispatched to the Nevada facility, where they discover that the female has hatched and is preparing to attack Las Vegas.
Serizawa objects to the military's plan to lure all three monsters offshore and kill them with a nuclear weapon, stating that the bomb will have little effect on the monsters and that Godzilla is just there to kill the MUTOs and restore balance. However, Serizawa's pleadings go unheeded, and the military executes the plan, which backfires when the male MUTO steals the armed warhead and delivers it to the female in their nest in the heart of San Francisco. Following this, Admiral Stenz agrees to Dr. Serizawa's proposal to withdraw military forces from the MUTO's destruction and give them over to Godzilla. Serizawa tells an extraction team that the MUTOs have likely laid eggs underground and are keeping the warhead there after Stenz refocused military efforts on retrieving the device.
Serizawa and Graham gather around Godzilla's presumably lifeless body in the remains of San Francisco after the battle. When Godzilla stirs and returns to the sea, Serizawa rejoices as the monster he has spent so many years studying returns to his natural habitat in peace.
Godzilla: King of the Monsters[]
Serizawa, Graham, and Monarch's technology director Dr. Sam Coleman are called to talk before Congress about whether Monarch should be placed under military jurisdiction five years after the Titans were revealed to the public. During the conference, Serizawa and his colleagues learn that Emma and her daughter Madison have been kidnapped by eco-terrorists led by crazy ex-colonel Alan Jonah, and they need Mark's help in rescuing them.
Serizawa and Mark insist that G-Team leader Diane Foster not attack when Godzilla gets too close to Monarch's Castle Bravo headquarters. Shortly after, Godzilla swims towards Antarctica, trailed by Monarch. It's here that the gang sees Emma burn Outpost 32 in order to awaken Ghidorah, who then has a brief struggle with Godzilla before devouring Graham, much to Serizawa's despair.
The Monarch team receives a video message from Emma on their emergency channel the next morning. She confesses that she's been working with Jonah all along and has a plan to awaken the Titans so humans may learn they were never the dominant race and save the world from the harm mankind has caused. Serizawa chastises Emma for endangering billions of people and attempting to manage something beyond humanity's control, but Emma challenges Serizawa's assertion by claiming that if the government had its way, the planet would continue on its path to doom unless the Titans are liberated. Emma continues her strategy by choosing to awaken Rodan from Outpost 56 on the Mexican island of Isla de Mara. Before Rodan awakens and decimates the settlement, Serizawa and his crew dispatch the G-Team to the island to begin evacuations. The gang then realizes Ghidorah is on his way to the island. Rodan and Ghidorah are lured together by the USS Argo to combat each other. The strategy works, but Ghidorah rapidly overwhelms Rodan and turns his attention to the Argo. Godzilla comes out of the ocean just as Ghidorah is about to reach it, attempting to subjugate him by biting off one of his heads in the process. The military then intervenes, sending the Oxygen Destroyer to destroy the Titans. Godzilla appears to be destroyed in the blast, but Ghidorah survives. Serizawa can only sit in disbelief at the outcome.
Ghidorah then regrows his severed head and lets forth a mighty roar, commanding the remaining Titans to attack humanity. Soon after, Monarch discovers that Ghidorah is an alien invader who wants to use the other Titans to terraform Earth into a perfect abode. Since the rivalry between Godzilla and Ghidorah was old and unique, Serizawa thinks that no other creature can fight back. While everyone is unsure what to do, Mothra arrives in front of Castle Bravo and reveals that Godzilla is still alive, but in a very weak state.
Serizawa, Mark, Stanton, and Dr. Ilene Chen plan to resurrect Godzilla by sending the USS Scorpion into the Hollow Earth and detonating a nuclear weapon in his lair. The launching mechanism, however, was destroyed during the submarine's collision, and the warhead can only be activated by hand. Despite the dangers of heat and radiation, Serizawa agrees to detonate the bomb in the hopes of resurrecting Godzilla. Before bidding his colleagues farewell, he hands over his notes and findings to Mark. Serizawa approaches the weakened Godzilla after braving the volcanic environment and activating the warhead on a one-minute countdown. Before the bomb explodes, Serizawa rests his palm on Godzilla's snout and bids him farewell. Although Serizawa's death was not in vain, it was revealed that his sacrifice allowed Godzilla to defeat Ghidorah, effectively ending the three-headed Titan's reign of terror and letting Godzilla to take his rightful place as the genuine alpha Titan.