Fuguu Ouji wa Tensai Renkinjutsushi

A man whose greatest dream was to experience the warmth of a loving family is reincarnated into the magical Iscalion Empire as Prince Asha, the unwanted eldest son. Deemed too tainted by his own bloodline to ever inherit the throne, he is isolated from his younger brothers from the moment they are born. Rather than fighting for a crown that rejects him, Asha relinquishes all royal ambitions and embraces his newfound freedom. He turns his attention entirely to alchemy, treating the discipline as his personal playground. However, armed with an overflowing natural talent and the retained knowledge of modern science from his past life, his casual experiments begin producing world-shaking technologies by sheer accident. His remarkable inventions effortlessly humble even the most arrogant nobles, inadvertently drawing him into the very imperial succession war he intended to avoid. Before long, the prince who wanted nothing to do with politics finds himself unintentionally dominating the struggle for the empire. Yet beneath his accidental rise to power and revolutionary discoveries, his deepest wish remains heartbreakingly simple: he only ever wanted the chance to be called "Big Brother."