Long story short, when she died in the 1st life, Claude was really devastated that he shallowed the devil’s heart(which has powers over space & time) in order to give Ivona a 2nd chance to live which is also why there’s a black smoke that surrounds time to time & the main reason why he can’t use his sword is b/c when they went into that ruined temple, that pillar that Ivona touched awakened the devil’s power that’s inside him. So the sword rejects him b/c of that. BTW don’t trust the temple they shady as f*ck.
If u want more details scroll down
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Ok so on to the back story, in the past life during the war against the demons, the aristocrats didn’t want to go to the front lines & they kept complaining & muttered that since they have the duke, he should be enough. Since he was the owner of the sword & was he’d save the world. When Ivona heard it all, she was furious, and told them off saying he is also human. But she didn’t know that Claude heard her words. And ever since then, he became curious about her. Can’t remember much but around the time he got curious about her he was already falling for her. This part is the part that was shown already in one of the chapters about doing the experiment and going to war so I’m just kinda gonna skip that part. After the war ended, he could’ve asked for anything since he stopped the devil’s resurrection, but all he wanted to do was treat Ivona’s ailment. But when he went to the high priest, he told him that it was useless since she was going to die soon. So when Ivona died he considered it the worst day of his life. He knew everything that happened to her, how horrible her life was. So when the priest asked him if he loved her he didn’t think so since he doesn’t know how to love. The high then suggested of a way by eating the devil’s heart, Claude would be able to give Ivona a chance which he agreed to & that’s how she was able to go back in time it was all b/c of Claude.
Is it just me or the Duke might be the resurrected demon king since the holy sword rejected him and all like didn't someone talk to him at the ruins that's why theres sum black smoke surrounding him or is he gonna be use as a sacrifice to Ressurect the demon king or smt like I have an eerie feeling about this lol I might be wrong since I didn't read the novel but like there possibility right?? Anyways that's all lol