Copypasta: Most of Clive's character development is based on his relationship with Joshua. You are seeing a character destroyed by trauma regain a sense of self. It is about finding his identity because up to that point his whole identity revolves around Joshua. Why? His father told him to protect Joshua, his mother thought he was useless and the only worth he has was him protecting Joshua. He felt sad that he didn't live up to everyone's expectations by not becoming a dominant and decided he could protect his country by protecting and serving his brother. It was the only thing that gave his life meaning. This is toxic because Clive is not living for himself, he doesn't really have an identity besides being Joshua's shield.

Now that he grows up, the realgame starts and he is an empty shell only driven by avenging Joshua. Once he sees Jill he remembers that there are others besides Joshua and rediscovers who he was before. He is Clive, not a slave named wyvern. You see his character grow and he is no longer suicidal. He accepts that Joshua is dead and learns to move on. That there are other people worth fighting for that he learns to form strong bonds with. He develops a strong goal in life and he decides to do good for the world in order to make up for his past sins

Then Joshua appears and he basically has to relive his trauma because he has to face the possibility that Joshua is going to die again. Now Clive is focused on selfsacrificing himself so that everyone gets their happy ending. Joshua notices this and punches him because he wants Clive to rely on him too. So what happens?Joshua dies and he mourns again, gets a good cry and then he stands up and fights again with determination. He basically gains the mental strength to live on for himself, he is no longer the empty shell he was when he lost his brother after phoenix gate so he picks up his sword and faces ultima. He finds worth in himself and uses his powers that made him feel like a monster for good