An indistructable item- Grimoire

The book itself seems nothing different from an ordinary book, if not for the fact that Rio knew about it beforehand, he wouldn't have been able to find anything wrong about it.

'i should go somewhere with less people first...' (Rio)

After paying the bill which that careless girlfriend of his forgot, Rio left silently. After reaching a particular hidden corner and confirming that no one was here, he brought out the book.

While holding the book he pulled out his sword and 

[Elemental sword Art: Blazing fire]

The book was immediately reduced to ashes in just a fraction of a second. 

After destroying the book Rio immediately backed away a few steps, and waited, he waited to confirm his doubt, and just as he thought the weird thing indeed happened...