Though Gundam Plastic Models, better known as Gunpla, exploded in popularity with the release of the anime series Mobile Suit Gundam, their presence faded before resurging with a new purpose. Through the power of Plavsky particles, fans are now able to pit their Gunpla against others in a virtual reality-style battle with the best competing at the annual Gunpla World Tournament. Sei Iori, whose father was a once finalist in the competition, dreams of one day conquering the contest himself. However, while Sei is an expert Gunpla builder, he lacks the prowess to effectively fight his creations during actual battle. In comes Reiji, a mysterious boy who is curiously ignorant of society but quickly demonstrates to Sei tremendous ability in Gunpla battles. The two boys decide to combine their strengths in order to sweep the Gunpla World Tournament and take the Gunpla world by storm.

Grade schooler Yuuta Tomonaga stumbles upon Deckerd, a humanoid robot under construction by the Japanese police, built to fight advanced forms of crime. Yuuta's constant contact with Deckerd gives the robot a "heart," or personality; when Yuuta is recruited as the "boss" of the "Brave Police" as a result, a true human/robot partnership occurs.

A great war occurred in the 20th century between humans and monsters. Since that time, the monsters rule the world in fear but keep relatively hidden from public view. A boy named Bokka ponders the past and wonders what became of the Meros Warriors who defended the world so bravely against the demons. He soon meets Kurofune and learns of the power of the Meros and the I-bar machines they ride in battle. Warriors are the only ones who can see and hear the Melody of Oblivion, a phantom girl hidden away waiting to be rescued and be the savior of mankind. During a battle between Kurofune and a demon, Bokka discovers something only his wildest dreams could possibly imagine...he too can hear that melody. Throughout his journeys, Bokka meets many monsters and their agents, friends, and companions as he discovers the true extent of his new powers. He must continue to battle evil in the hope of releasing Boukyaku no Senritsu and free a world that has forgotten its once beautiful melody.

Dr. Hell and his Mechanical Beasts are back, and they're more dangerous than ever before. Kouji Kabuto and Tetsuya Tsurugi fight a fierce battle against these hellish machines, which are under the command of Baron Ashura. Unfortunately, they are defeated, with Kouji's Mazinger Z being captured and Tetsuya's Great Mazinger seriously damaged by the enemy. The devious Dr. Hell quickly converts the captured robot into Ashura Mazinger and uses it to attack the Photo Power Lab. At the same time, Kouji is missing in action, which leaves Testuya to defend the lab in the damaged Great Mazinger. But the forces of Dr. Hell are too strong, even for a brave pilot such as Tetsuya, and all seems to be lost. The battle seems to be drawing to a close, until an overpowering blast fired by an unknown robot destroys the entire Mechanical Beast army. Could this mysterious robot be the legendary Mazinkaiser, and who is piloting it?