Stick to his original plan -- steal.

Samael's book of adventures was something Samael considered a memento. The reason, even when the Duke's mansion was burned down before his long slumber, he rewrote it and kept them. He didn't bring a lot of things to the mainland, but those books were with him. 

They were that precious. 

After all, those books held knowledge and information about how vast this mysterious world was.  There were many things to learn and many interesting creatures who had wisdom that no one else had. Those books were very close to his heart. It was a book to open someone's mind that there were many things to learn in this world.

To think that someone dared touch the stories he had written, twisting those stories in their wicked plans, giving a bad image to those things like the Kraken, and impersonating a plague that killed many good souls was an utter mockery. 

Those things weren't something to make light of. Not the life of the dead, and those living. 

SPLASH!