Because Seb was the caretaker of the forbidden library, he had led his life under a lot of responsibilities and restrictions. So when he died and his skill activated to give him a second chance in life, he decided to live his second life as his heart desired.
That was not a bad line of thought. Elena agreed that people should live their lives as they wishes. But this perspective became problematic if the person in question had evil intentions and desires. And that was exactly the case for Seb.
In his second life, Seb had became completely unrestrained. Even though his level was low, he still had access to most of his skills with his intact soul. Not only that but his stats were also higher than normal because of his special situation. For all these reason, against anyone whose level was not greatly higher than his, Seb was an invincible existence.
