Taiworld Manga

The story follows the adventure of twin siblings who aspire to become Heroes, exploring a Fantasy, industrialized-era world. On their very first mission, they were attacked by an Earth Bear controlled by the New Era People. The younger brother ended up getting killed, but he has resurrected into a different body thanks to a weird guy who was presented at the scene. In exchange for the contract over the siblings, the weird guy promises to help to turn the younger brother into the strongest person in the world...