Not literal brothers. The MC was transmigrated into a story in which they were raised as half brothers. But it's revealed early in that there is no actual blood relation as they have no parents in common. (MC was a product of infidelity on the mother's side.) This is also only one of MANY worlds that the MC and ML transmigrate into, where they have entirely different relationships within the plot each time. Only the first setting has an incest-adjacent relationship setting. The rest of their roles have zero familial ties.

wait- can someone explain this to me plz? Aren't they originally brothers? (srry I dropped it 2-3 years ago)