Echoes of the Imperial Sun / taekookff

A brilliant strategist dies defending his sworn brotherhood in a bloody rebellion, only to wake up five years later in the body of a frail, low-ranking noble's son. Seeking a quiet life, his plans are ruined when his former best friend—now the brooding, feared Crown Prince—notices the "frail noble" using military strategies that only his deceased soulmate ever knew. The prince becomes obsessed with uncovering the noble's true identity, while the strategist must navigate the very court that betrayed him. Reincarnation/identity reveal, slow-burn angst, shared history, political chess match.