MC is the son of a rich man who ran away from home to marry the woman he loved. They adopted the original protagonist to keep company to their son but the wife dies soon. Father goes out of control, gambling, drinking, staying out all night and day cause his son's face reminds him of his wife. Originally the protagonist framed her brother and had him killed, but with the MC arms und it doesn't happen. Dad comes to his senses and returns to his home with his kids. ML is MC's cousin and also the original male lead. Everyone loves the adorable MC but are wary of the protag and the greedy look in her eyes. Eventually protag looses it and tries to have the MC thrown into the ocean and killed, MC is assumed dead by everyone but in reality ML has found him and is keeping him locked in his mansion. MC eventually realizes that ML let legs be ruined on purpose because he lost his mind and is afraid of MC walking away. MC leaves world after years when protagonist commits suicide.
MC is a person killed by the protagonist who is a ghost killed by his ancestors. MC turns into ghost and is found by the ML who is also original ML. Originally he killed MC because he was in love with protag but this time he doesn't fall for her. Stuff happens, ML dies of old age and MC leaves the world after he is gone.
MC is a beast hybrid. His father is killed by light priests but not before he explodes himself to kill them as well because he thinks that his wife has been killed by them and he wants to give his son the time to escape. Turns out wife wasn't dead and faked her love for dad because she wanted a powerful beast son who she could form contract witha nd completely control. MC escapes into the forest where he is adopted by these old trees and eventually the entire forest and other beasts dote on him since he is the most powerful beast cub there. He saves ML who is the protagonist and brings him back to his home. Stuff happens.
MC is the child emperor and ML is the ML original. He is the regent, basically the emperor is his puppet. Protagonist is a young concubine born daughter from the prime minister's home who ML originally fell in love with because she looked similar to the MC (who he had dreams of). ML falls in love with MC after he meets him after transmigration, whole heartedly decides to make him the emperor while he decides to just be a loyal subject. Prime Minister's daughter appears, reclessly drives her carrige in the streets and almost tramples the emperor who is undercover as a commoner, ML is super worried and pissed. Sees ML and tells maid that she'll marry that man. That night ML goes to her house and has her family killed right when she was acting spoiled and asking her dad to marry her to the regent. Eventually ML goes to conqure trouble area to give to his emperor, ends up getting scared across his face but wins. Is afraid that MC will not like him anymore, uselessly worries and hides in his courtyard. MC comes and after bantering and calling him a perv, he tells ML that he'll just go and fill his harem with beauties since ML isn't interested in him anymore. ML comes, is assured by MC that he still love's him. Regent dies, MC joins him.