The planet Rosetta has been taken over by the Black Star army led by Captain Dagger. Takashi Shishido and his mother Rosemary escaped to Planet Earth after his father Gou was captured by Dagger, who is actually Takashi's evil twin brother Hiroshi! While living peacefully on Earth, Takashi attends a kung-fu school in Japan, and has four friends, but they had no idea that he was from another planet, a secret only his martial arts teacher Takamine knew. But when Captain Dagger initiates his attack on Earth using his army of various giant monsters, Rosemary (who also goes by the civilian name "Mari") gives Takashi the Megalon-Bracelets, with which he can transform into the giant long-haired warrior Megaloman to fight the evil monsters for the protection of Earth. Early in the show, Takashi's four martial arts school friends, Seiji Kurogawa (a tough, Bruce Lee-like fighter), Hyosuke Yuri (the comedy relief), Ran Takamine (Master Takamine's daughter & Takashi's girlfriend) and Ippei Saru (the little kid) discover his secret and Rosemary decides to invite them to join Takashi in battle. So she gives them their own Megalon Bracelets to transform into a quartet of multicolored martial arts super-warriors to fight alongside Takashi!

2062年，为了轨道电梯的所有权，地球分为两大阵营而互相争夺；主角桂木桂隶属的自由宇宙军，计划以新研发的D兵器“时空震动弹”破坏轨道电梯的能源供应，但是行动遭遇到敌对阵营的猛烈炮火而不得不撤退，危急中怒火中烧的桂木桂，启动了尚未调整好的时空震动弹，结果引发了始料未及的时空混乱，造成多元世界同时出现互相混合，并形成了“相克界”，桂木桂也因此被卷入震波而时空转移，来到了事件发生的20年后的混乱时空世纪20年。
桂木桂被埃曼人（エマーン）的商队寻获并一同行动，但是桂木桂却由于身为修复混乱时空的关键“特异点”，因而成为各势力争夺的目标；在不断战斗与寻求解决之道的同时，桂木桂官校的同窗欧森竟然出现在眼前，并且与他兵戎相见；甚至还见到了自己未来的女儿雅典娜。桂木桂最终将面对新旧交杂的世界，并试图修复时空混乱的局面。而桂木桂终于发现，要想让时空回归正轨的最后手段，竟是得前往当初时空震动弹启动前那一刻的时空中，并杀死当时的自己…　　

故事的主角春日恭介，因为其家族春日家拥有超能力（超能力来源是母亲的家系，父亲是普通人），每当被人发现其家族秘密便需要搬家。这次因为他的妹妹春日久留美在运动会运用超能力，在3秒内跑完100米，使他们不得不搬第七次家。

刚转入新学校的春日恭介，在一条长楼梯邂逅少女鲇川圆，后来发现是同班同学。另一方面同校学妹桧山光，自幼便认识鲇川圆，因为某个契机而对春日恭介产生好感，三角恋情就此开始。