Fuguu Ouji wa Tensai Renkinjutsushi

One day, a man obsessed with warm, loving families gets reincarnated into the magical Iscalion Empire... as Prince Asha, the unwanted eldest son. But he's too "tainted" by his bloodline to be an heir and is separated from his younger brothers since their birth. So, he gives up on attaining the throne, embraces freedom, and dives headfirst into alchemy as his personal playground. But with his overflowing talent (and memories of modern science), he ends up inventing world-shaking tech by accident?! Even nobles get smacked down by his "inventions". Before long, he's unintentionally dominating the imperial succession war. "All I ever wanted... was to be called 'Big Brother' someday." ___ * (https://ncode.syosetu.com/n1454hs/)