Strongest Survival by Otome Game’s Heroine (LN) - Chapter Volume 5 3: Royal Sorcery Academy

Void plane: synonymous with terror and taboo, no one knows how big the void is, because it is growing every moment, and anyone who talks about the void will be shocked.

Void Lords: The voices of the Void plane, the plane’s invaders, conquerors and destroyers; they lead the Void’s armies all the way to war, and when they discover a new plane, they will do everything possible to pull it into the Void embraced by the Void’s reward.

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- Description from novelbuddy

Leon and his father, Artorias, are the last remaining scions of a once powerful and illustrious family of lightning mages. After barely surviving an attack that destroyed their home fifteen years ago, they now live in the dangerous Northern Vales, a desolate wilderness far away from civilization. But those who want them dead are strong, patient, and relentless, and it is only a matter of time before they find the two they seek...