Reread the novel and yes he killed Eochaid only after utilizing Claiomh Solais's full power he even said he can only use it for a few seconds the reason he complemented Korin was because Korin was able to go toe-to-toe against him in pure skill and eventually overpowering him, Eochaid was strong because he was the user of Claiomh Solais in the last iteration but without it he's just a bit weaker against Korin

She had an okay character development but that only happened after the demi-humans went extinct

She just wants to get revenge on demi-humans because they killed her mom

He used it against Miruam to protect the demihumans and then turn them into citizens so that she cannot harm them

Basically when 10 seconds had passed every constellation from historical grade to myth grade had tried to peak in his character profile and used their authorities which forced him down and made him unconscious. The Fourth Wall is someone else from the previous regression - Revealed in the Epilogue. He also met a younger Dokja Before the Epilogue. I can't really say anything more because this is already to much to comprehend for someone who hasn't finished the novel. All i can say is the Fourth Wall is the one who answered Dokja's message in the subway in chapter 1 but he did not write TWSA

So basically he looked at his profile for 15 seconds the Fourth Wall said only for 10 seconds after 10 seconds every constellation was trying to look at his profile as for the second part of your sentence he is the character himself the Fourth Wall is someone who turned into the Fourth Wall because someone said to protect Dokja - Epilogue. He also met himself but a different Dokja - Last arc before the Epilogue