Metal Bat is irritated with his special assignment of protecting two important Hero Association associates, Narinki and his son, Waganma. They are eating at a restaurant in S-City called Mouse Sushi, when suddenly, two monsters erupt from the ground. The monsters are Junior Centipede and Venus Mantrap, who've come to kidnap Waganma. Junior Centipede holds Waganma hostage, and Narinki begs Metal Bat to save his son. Junior Centipede recognizes Metal Bat as an S-Class hero, while Venus Mantrap tells Junior Centipede to take Waganma and leave. However, Metal Bat grabs his coat and his bat, assuring the monsters they won't set a foot outside the restaurant.
An off-screen battle takes place, and Metal Bat is seen standing on top of the corpses of the two monsters, eating some sushi that was prepared nearby. Narinki and Waganma are amazed by what they saw, and Narinki takes a photo to remember this moment. Metal Bat urges the two to leave and find cover. As Junior Centipede is dying, he speaks to Metal Bat and tells him how powerful of a hero he is. But as Junior Centipede speaks, he calls out Metal Bat's excessive confidence, telling the hero he was once the same way, believing himself to be the strongest. This changed when he met his master. Another monster erupts from the ground, destroying the restaurant.
Metal Bat is barely able to grab the two males and is thrown back several dozen meters. The monster turns out to be another centipede, except he's twice the size of Junior Centipede and is blue instead of red. Metal Bat notes this, but then, from the sewer, a strange gas fills the air. Narinki and Waganma are knocked out by this gas, while Metal Bat remains diligent. A monster with vines comes out of the sewer, and it soon reveals itself as a plant-like mysterious being named Rafflesidon. Metal Bat declares he will crush the monsters and extends his bat for battle.
Rafflesidon attacks Metal Bat with its tentacles, but the hero manages to deflect and destroy the tentacles with his bat. Senior Centipede follows up by striking Metal Bat with his Centipede March. The hero blocks the attack, although his clothes are severely damaged in the process. Metal Bat swings his bat to ward off the monster and jumps back several meters. The monsters admit Metal Bat's impressive abilities, while Metal Bat asks them why they're after Narinki and Waganma. Rafflesidon laughs and says they'll disclose that information if he defeats them. Metal Bat begins to falter, and Rafflesidon notes his sleeping gas is finally kicking in.
Taking advantage of the moment, Senior Centipede rushes Metal Bat and strikes him several times across the face with his legs. Metal Bat is unable to fight back, slowly losing consciousness, and is hit again by Senior Centipede with its body. The hero is sent flying back, and is once again pummeled by several more attacks, but in a surprising twist, Metal Bat hits himself in the head. Blood begins to flow from his head and his nose, and Senior Centipede wonders if Metal Bat has finally lost his mind. He lashes with his front leg, but this time, Metal Bat retaliates, swinging his bat and dismembering the leg from the monster's body. Metal Bat remarks that he feels much better, while Senior Centipede realizes he's become more powerful than before.
Likewise, Rafflesidon doesn't understand how his sleeping gas could wear off so quickly, so Metal Bat gives the simple explanation that if he can pump himself up, he can handle pretty much anything. Metal Bat states that the two monsters had given him some serious damage before, but that since he was a nice guy, he'd end both of them with a single blow. He proceeds to kill both Rafflesidon and Senior Centipede with single swings, and with Senior Centipede, the force of the swing is so strong, his entire body begins to crack and explodes in a mixture of green blood and blue body parts, making Metal Bat the victor.
As Metal Bat is walking away, he remarks that he hasn't been this pumped up in a while. He then recalls he forgot to ask the monsters about their motives. He looks at Narinki and Waganma and wonders if he should wake them up by hitting them. Suddenly, two heroes, Mohican and Pineapple, come to assist Metal Bat. The hero says he's already handled the threat, but they could take Narinki and Waganma to safety. Without warning, the ground begins shaking violently, and a final centipede monster many times larger than Senior Centipede bursts out of the ground.