A few years back, I read an isekai-type manga/manhwa/manhua (most likely a manga, but I'm not sure).
The setting is in the medieval era, I guess. It was about a noble teenage boy who is considered weak (if my memory didn't betray me, he was ill) who has (maybe) two siblings from a different mother.
This stepmother always planned to kill him to prevent him becoming the head of the family. Little did they know, he wasn't sick anymore.
In a fight scene I recalled, this boy unleashes an awesome AOE skill called 'God's Territory'. This and that happened, and I forgot the title of the manga.