Fuguu Ouji wa Tensai Renkinjutsushi: Koutei nante Gara ja Nai node Teimai wo Kawaigaritai @COMIC

One day, a man who longed for a close-knit family was reincarnated in the Iscallion Empire, a land of advanced magic. His name was Asha. The unfortunate first prince was unable to become the eldest son due to his lineage, and was destined to be shunned by his beloved younger brothers. So he decided to give up the throne to his second son and enjoy the freedom of pursuing his alchemy hobby. While spending his days immersed in experiments... his overflowing talent and scientific knowledge suddenly led to a great invention!? He also accidentally defeated a prominent nobleman and even came to dominate (?) the battle for the throne. "I'd like to be called Big Brother someday," says the laid-back older brother, who unconsciously takes control of the empire for his younger brother in this heartwarming brothers' fantasy! (Source: Comic Corona, translated)