To be fair it was mear speculations and the nose actually look the same and the protagonist can time travel so the culprit being another version of himself is not impossible. We barely even get any screen time of the main antagonist aside from being the mysterious hooden man.
The main...
The author just can't decide whether he wants Rubia in the story or not..
The author tried many companions with the mc but it seems Isaac might be the one that would stay.
My theory is that it's actually him since the nose is the same. This version of him might had just did exercise or workout to get buff and no longer look fat.
@YamiMao
I see then I would suggest to keep calling the Demon race as is while the so called demons be called fiend but greater demon does sound better than high demon.
I hope my comment was not misunderstood as me trying to be rude.
I was just giving suggestions and the final decision still...