A new landmark has sprung up in the city, in the form of a giant mushroom-shaped Heterodyne. The Heterodyne has been there for a week, and, aside from regenerating itself when the army first attacked it, it has done nothing. Nonetheless, Dai-Guard is expected to remain on permanent standby whilst the army and Tech Division observe the creature- and that means everyone has to spend long hours sitting around and doing nothing.
As a break in the routine, the team are allowed to go and eat in pairs, and Akagi is unfortunate enough to be paired with Shirota; insisting that they eat together so that they can both be contacted easily, Shirota takes Akagi to a seafood bar for a quick meal. Whilst they eat, Shirota explains the problems he has with Akagi’s “act first, think later” attitude. When the tactical advisor tries to deliver a speech on how employees should follow orders, however, he finds his word pre-empted by someone behind him- a different supervisor talking to one of his own employees!
Whilst the rest of the team endures the boredom of being on standby, Domeki, the genius head of Tech Division, decides to take a break from her analysis to head for the public baths. Meanwhile, Shirota continues to hold forth with Akagi- his view is that everyone should stick to their own job and not try to take over others’ roles. Shirota is quite willing to leave piloting Dai-Guard to Akagi, so Akagi should leave strategy and tactics to him. Akagi doesn’t seem too happy about this stark assessment, but before he can say anything, the restaurant starts shaking. The Heterodyne has activated.
All around the mushroom Heterodyne, smaller mushrooms start sprouting up out of the ground. Dai-Guard is knocked over by the tremors, whilst the army begins evacuating all civilians from the seafood bar and nearby shops. Leaving the restaurant, Akagi hears a woman asking the army to help find her trapped dog, but before he can do anything to help, Shirota calls him away. They have to get back to Dai-Guard.
Once again, the army tries firing on the Heterodyne, but it responds by regenerating and creating more mushrooms. Whilst the others try to get Dai-Guard upright again, Shirota calls to say that he and Akagi are on their way. Even as Shirota makes the phone call, however Akagi hears an army officer order his subordinates to abandon the woman’s dog, and makes a decision- if no one else will help, then he will go back and find the dog himself.
Searching the area, Akagi eventually locates the dog, only to find that it is trapped behind a locked door. Whilst Akagi tries his best to prise the door open, the army continues its attacks. However, for every small mushroom they destroy, three more take its place, and firing at the main Heterodyne only causes it to retaliate by creating long and sharp vines that attack the army helicopters.
Accompanied by two soldiers, Shirota manages to locate Akagi, who is still trying to rescue the dog. Akagi refuses to let go of the pole he is using to open the door, so instead, Shirota and the others stay to help him. Together, the four of them finally manage to get the door open, and the dog is retrieved. Akagi is now ready to go back, but even as they turn to go, the ceiling above caves in. Pushing the others out of the way, Akagi is caught in the cave in, and ends up buried in a pile of earth. Akagi is dug out easily enough, but, thanks to the fall, his leg is injured.
Having taken her laptop to the baths with her, Domeki has finally finished her analysis, and calculated the Heterodyne’s weakness- attacking a specific red hexagon on the main body should destroy the whole thing. The information is relayed to Oosugi and the team, and Dai-Guard is prepared for battle, Unfortunately, Akagi’s injured leg means that he can’t pilot it directly, but he can guide his replacement- Agent Shirota.
Even Shirota has to admit that there is no time for advanced tactics- they will have to employ Akagi’s simple plan of going in fast and hoping they can land the first blow. As the army creates a smokescreen in the hopes of hiding Dai-Guard from whatever senses the Heterodyne may possess, Shirota takes the place of main pilot, with Akagi in the cockpit with him; under Akagi’s guidance, Shirota moves Dai-Guard (equipped with drill arm) in for the attack.
Running towards the Heterodyne, Shirota activates the drill arm, and targets the weak point. Before the blow can land, however, the Heterodyne sends out a vine that severs the drill arm and sends it flying. Not only did the attack fail, but now Dai-Guard has lost its main weapon.
The Heterodyne follows up by sending out more vines, which Shirota has to quickly block with Dai-Guard’s one remaining arm; even so, enough damage is done to take out the external monitors, leaving the pilots blinded. Without being able to see, there is no way to attack, so Akagi blows the hatch on the cockpit, restoring visuals but leaving them exposed and vulnerable.
As the Heterodyne launches another vine at Akagi and Shirota, Akagi orders the tactical advisor to catch it with Dai-Guard’s arm. A sceptical Shirota doesn’t think that he can do it, but with encouragement from the other pilots, he manages to catch the vine right before it skewers him and Akagi.
As Shirota rips the vine off, Akagi steps forward to get a better view, so that he can guide Shirota. Following Akagi’s instructions, Shirota repositions the vine and slams it down into the Heterodyne’s weak spot. As he does, the hexagon shatters, and the entire Heterodyne explodes into white vapour.
As always, things aren’t quite over yet. Even as Shirota relaxes, Dai-Guard loses its footing, and Akagi falls out. Seeing him fall, Shirota manages to make Dai-Guard reach out and catch the main pilot in its hand. Much to Shirota’s relief, Akagi comes through unharmed, and a lot less shaken than Shirota himself.
Back at 21st Century Security HQ, Domeki presents her findings to President Ookouchi. The pink/red hexagon that creates a Heterodyne is known as a fractal knot, a central nexus that replicates itself and combines with the surrounding elements to form the Heterodyne’s body. Destroy the fractal knot, and the Heterodyne itself breaks down- this is what Dai-Guard has been doing (by accident or design) since its first battle. It is good to be aware of this weakness, but Ookouchi only wishes they had known about it when the very first Heterodyne attacked twelve years ago- then there would have been no need for the OE bomb.
As the Dai-Guard team clears up and prepares to go home, Akagi asks Shirota how it felt to pilot Dai-Guard and save the day. Shirota claims not to remember much about it, much to Akagi’s relief- he didn’t want Shirota coveting his job. However, as Shirota glances away, he clenches his fist as if reliving the moment when he made Dai-Guard’s hand catch Akagi. Maybe he wasn’t as unaffected by the experience as he claimed…