Demon Slayer: Ci of Thunder

He once lost everything and vowed to protect the present with thunder, He is extremely talented, but he is destined to play the prelude to parting. "Brother, take care of grandpa." Infinite City, "Who am I supposed to be? Isn't this the trash that doesn't speak?" "Brother, I'm here to catch you." (Parallel time and space, non-travelers) (The growth flow will be a bit sadistic, but I hope I won't have any regrets after the protagonist becomes capable)