Hunter x Hunter: Sun Breathing

Roy always appreciated a methodical approach to life. He believed in taking things one careful step at a time, building a stable foundation for a predictable future. That all went out the window when he was reborn as a Zoldyck. Now, his life is anything but predictable. He has to navigate a new existence with: A stoic father whose love is measured in combat prowess. A psychotically overbearing mother who thinks torture is a form of affection. A gallery of twisted siblings, each with their own unique brand of deadly obsession. A grandfather whose daily exercise is a professional assassination contract. ...and a seemingly immortal great-grandfather who pretends to be senile, but is secretly using a mountain-sized En to spy on the entire family while "watching cartoons." Reborn into the world's most infamous family of assassins, Roy must trade his quiet, orderly life for one of constant survival. Armed with the memories of a strange breathing technique from another world, he must forge his own path in a family where weakness means death. One careful step at a time. ~~~~~~~~~~ — Description from novelcodex.org