Regarding aethernitas, I agree what lucas did was wrong but he used black magic to quell his feelings too so I doubt he could feel any emotions.. it was wrong thou but whatever path aethernitas took after that was his own choice. He had the choice to be good or evil but he took the latter path. Sure, Lucas may have been the catalyst but the choice was his. It is his cross to bear.
You see when your life is already chosen for you and Lucas going on rampage holding people life by a string and scissors ;Aetherinitas didn't have much of a choice since what Lucas said affected him greatly and could not change his path even if he left his kingdom. Aeternitas wanted to hear Lucas say those words but infront of the people who abandoned him and made his life miserable which is why he said "I almost fail for it, and almost forgot the reason why he wanted revenge" so he was technically still holding truth to his feelings
It's understandable why he was sad but at the end of the day, it was his own choice.
Ok after letting it marinate I can FINALLY UNDERSTAND.. This problem started BECAUSE of Lucas (hear me out) ..Lucas was well seen as a type of guardian God in the past any word that comes from his mouth could mean the future to someone. All though Aeternitas died without being able to explain himself why he became an evil spirt it was very well clear that Lucas calling him the weakest created bad rumors thus creating a hell path for him so he tried to take revenge by taking his mana (which he succeeded but somehow went wrong when he couldn't handle it).Aeternitas then became and evil spirit still trapped in the kingdom hoping to meet Lucas so he took advantage of the Claude older brother who was strong and suffering and took over his body.. it may not be clear but Claude older brother never had the intention of killing him causes he kept choosing death everytime rather then trying to kill him.. but Aeternitas needed someone of weak heart to be able to control .. now I also don't like Lucas that he keep calling jannette a chimera especially infront of Ezekiel... I also didn't like that Ezekiel said that he can no longer put her safety first because he is in love with the princess .. like bitch you said you see her as a sister then don't say stupid shit like that when all her life has been nothing but being a shut in now she actually felt like she really had no one ..you could of said "althoughi have feeling for her in my heart and eyes your are still importantto me because you are like a sister to me" jannette would of understand... now for the main character she really didn't do anything except try to copy Janette way of thinking (pure,nice,cute) every time she needed help she couldn't solve anything without Lucas or ijekiel... Claude is actually a good father but he couldn't live without his wife ..well bro idk you could of just choosen death instead of black magic but sure what ever make you forget her but you also forgot your child in that process .. so no your still an ass to the very end because even after regaining your conscious back you could of ended jannnette life too even though you know she didn't do anything wrong but only stopped because of your daughter smh .. poor Jeannette was the victim here