No CPR - Chaotic Isekai Wandering Chronicle

The death of a nationwide gang leader. In the wake of his passing, the eldest son, Do-gyun, and his half-brother, Seol—born into a Yakuza family—clash over the chairmanship of the Baekcheon Clan. Do-gyun, who has no desire to lead the organization, attempts to flee abroad, only to be stabbed in the back by Kang Ji-han, the right-hand man he trusted most. Facing death, Do-gyun is summoned to another world as a Hero... Do-gyun finds himself swept up in a struggle for the imperial throne. Then, following in the footsteps of his former subordinate, Chief Kang, and his half-brother Seol, even his middle and high school classmate, Se-geon, is summoned to this other world one after another.