Martial Arts! Purging the World of Corruption

(Older brother protagonist's satisfying power-fantasy antics + younger sister heroine adored by both men and women)

After a series of events lands the protagonist's family in the crosshairs of the local powerful, the entire family is murdered one night, leaving only him alive. By a twist of fate, he obtains an ancient, divine martial art. From then on, he sets out to uphold justice and defend the weak against the strong.