Read this manga when i was younger and can't seem to find it or even remember the name. Its like set in the future and a guy wakes up to find out he's in the body of a kid and i think he had like an excavator or a drill for an arm i believe. I remember him traveling trying to find and fight the other people that got turned into kids and that had metal body parts like him. Im pretty sure the main character was wearing like overalls, sorry if my description isnt a whole lot of help