If you're looking for manga similar to Megaton Musashi, you might like these titles.
K—an agile mech pilot in Neo Seoul police's high-speed mobile unit—specializes in chasing down and eradicating terrorists. His duty has always been to protect the citizens, and he's given little thought to the mega-corporations that run the city. But when an ordinary arrest explodes into a nightmarish battle, K is painfully forced to question his convictions. Stripped of all sense of right and wrong, K must make a terrible choice—either join his enemies, or lose all sense of justice!
Universal Century 0153. 17 years have passed since the "Steel Seven" defeated the remnants of the Jupiter Empire. As a new conflict brews between a Side 2 faction known as the Zanscare Empire and the League Militaire/Earth Federation a high schooler on Side 3, Font Baud, is hunted by Zanscare special forces when he discovers their secret Newtype weapon. However, he encounters a little girl, who is accompanied by a blind man and is rescued by the strange return of a mobile suit that defeated the Jovians.
Together with his robotic pet, atom, Sho Tobio travel from Japan to Dong Bei City in China. His mother is a scientist assigned to re-evaluate Japanese weapons left in China as the result of Japanese colonialism. Some of those armors are producing dangerous gas. Moreover, the sentiment for Japanese is stabbed inside local people’s mind. Atom is the only one he can talk to. One night, Sho was having a phone conversation with his grandma in Japan when the electricity blacked out. Suddenly Atom reacts into some transmission and runs away. Sho is trying hard to catch him. When he finally gets his hand on his dog, they’re already in some kind of basement. Right in front of their eyes lays a gigantic robot...
On the planet Zi, Zoids are no longer used for military combat; instead, they are now being used for sporting events known as Zoid battles. The Zoid Battle Commission oversees these battles, enforces the rules, and declares the winners. In the midst of fierce competitions, one team aspires to rise to the top: the Blitz Team! With the help of Bit Cloud and his Liger Zero, the Blitz Team will compete against not only regular foes, but also the talented Harry Champ and the criminal organization known as the Backdraft Group!
Perverted, cocky Ken used to live a normal life until several giant monsters crashed onto his city. In the midst of their carnage Ken’s secret crush was killed, and his grandfather seriously injured. Hope seemed lost for the inhabitants of the city and the world, until Ken discovered that he holds the key to summon the pilotable Beast-God Riger! Within the massive bio armor, Ken must now battle the invading monsters to protect Earth, and keep them from awakening a demon within the Demon Stone – a demon who will put a stop to all human life for good!