Ura Kagyou Tensei: Moto Gokudou ga Kazoku no Tame ni Ryouchi Hatten sasemasu ga Nanika? @comic

A yakuza who lived his entire life as a lone wolf is reincarnated into another world as Ryuu, the third son of a noble knightly family. For the first time, he experiences the warmth of a loving family and grows up cherished. However, he soon realizes that his kindhearted family, though strong in battle for generations, is hopelessly bad at business and incredibly poor! Deciding he has no choice but to step up, Ryuu first sets out to reform their finances. Utilizing his mysterious "Gokudou" skill and knowledge from his past life's shady dealings, he successfully sells the crops he cultivates. He even makes a fortune with a food stall at a local festival, launching one new venture after another. But as the family's fortunes rise, so too does the jealousy of worthless nobles who begin to hold a grudge against them. The curtain rises on a fantasy about fief management, full of duty and heart, starring a kindhearted former yakuza boy! (Source: TO Books, translated)