Agul vs. Gaia (アグル対ガイア Aguru Tai Gaia) is the eighteenth episode of Ultraman Gaia.
As seen in the previous episode, Agul brushes Gaia aside and opens up Zonnel's shell, exposing the light within to shoot out at Diglobe. Gaia, (knowing the risks from his computing calculations), immediately flies up and summons a huge energy shield to fling over the city as the resulting shockwave flashes over. Gaia is knocked from the sky, however, and Agul taunts him before disapearing. Even though his Color-Timer is rapidly flashing, Gaia flies Zonnel back to his cave as Team Crow observes.
Later, an exhausted Gamu is flying back to the Aerial Base, asking PAL to take over the controls. He is wondering about the device that was attached to Zonnel, and is examining it in his room on the Base when Atsuko and Georgie interrupt to celebrate Georgie's birthday. Meanwhile Fujimiya confronts Reiko about her comments about believing in the two Ultramen in a broadcast, and they discuss the merits of humanity before he walks off.
Some time later, a ball of blue light goes into Aerial Base. Gamu is sleeping when the device starts blinking, and realizes there's an intruder aboard. Going to the Command Room, he encounters Tsutsumi, Atsuko, and Georgie, who tell him they can't enter the room. Just then, the Aerial Base Repulsor Lift engines start to malfunction, with Gamu running off. Ishimuro appears with Chiba and three guards, and Georgie and Atsuko propose to reset the main computer in the center of the ship while Tsutsumi works with Team Seagull to figure things out in other parts of the Base.
As they all get to work, Fujimiya is inside the bridge declaring to further sabotage Aerial Base, when Gamu teleports in as Gaia. Fujimiya chides him for wanting to protect the threat to earth that is humanity, while Gamu/Gaia questions how and why Agul is helping him. Fujimiya transforms and they spar, Agul aiming for the computer equipment, but Gaia protects it. The members of XIG manage to get things aboard the Base functioning once more, and the guards burst in, just as Gaia opens a hole in the side of the Base. Chasing Agul, Gaia flies out and the hole closes just before one of the guards gets sucked out. Chiba wonders why the Ultraman were on the Base.
Gaia is flying looking around for Agul, when suddenly Agul appears giant-size and punches him out of the air. Gamu briefly untransforms but barely manages to re-transform before he hits the ground. Gaia gets up with his Color-Timer already blinking, and is again overshadowed by a giant Agul, who shoots power flares at him. Evading them, Gaia runs into a nearby warehouse and tries to grow to giant-size as well, but is unable to due to too much power use.
Agul shrinks to human-size and confronts Gaia again in the warehouse. They duel again, Agul trying to use his blade against Gaia, but this time Gaia is able to keep up with Agul, making his Color-Timer blink as he uses the Photon Edge to negate Agul's blade. Each then launches a beam-power attack at the other, and when that cancels out, use a kick attack. Red and Blue lights both flash out of the openings of the warehouse, and the two Ultras revert to human form. Managing to stand up, Fujimiya compliments Gamu on getting stronger, but tells him he will defeat Gamu for interfering in his plans. He staggers off, while Gamu asks out loud why the Earth gave Fujimiya Agul's power.
- Ultraman Gaia Volume 5 features episodes 17-20.
- While Hiroya was walking down a street, a restaurant had the name Eye Slugger on it in tribute to Ultraseven.