Avenger 1 is the third episode of the Planet With series. It aired on July 22, 2018.
Soya attempts to attack the leader of Grand Paladin in hopes of quickly ending the fight, but Takashi transforms into his own mech and fires a laser that damages Soya and his mech as it carves out a large section of the nearby cliff. Forced to take drastic action, Sensei summons his spaceship, which happens to be a giant mechanical version of himself, and places Soya inside. Soya has an odd dream where he sees Sensei arguing with a white, dog-like creature over the path of the Nebulans and his own fate. Soya then wakes up in his room, having been unconscious for three days. Soya quickly returns to school and gets roped into the school's Occult Research Club with Nozomi and a slightly flamboyant graduate named Seigi. Suddenly, the island is again under attack by a Nebula Weapon, this time in the form of a bunch of upside-down babies. Harumi leads the charge in this attack, and after the team locates the core, she rushes in to destroy it, hoping to avenge Miu's defeat. She manages to destroy the core, though after the explosion, Seigi appears unconscious and unarmored.