Looked through the instruction book and tried some internet searching but got no results. Not sure if anyone here happens to know how. 
In case the Gen. Discussion glitch strikes this goes in the 3D Dot Game Heroes forum.

You mean how you register them in the Bestiary? If you want to know, put it in as a spoiler because it sort of is: 
 

Oh, and Gatero might not be the correct name of the town in the US release. I got this info from EgHeadFoo's awesome faq on GameFaqs. If you have any more questions I think he's pretty much got everything answered in his FAQ.

" You mean how you register them in the Bestiary? If you want to know, put it in as a spoiler because it sort of is: 
 

SPOILER WARNING: Click here to reveal hidden content.

The Bestiary is an equippable item that can be obtained by trading the Small Ring found in the Desert Temple to the redheaded girl up by the northwest house of Gatero. It works much like a sword, in that you use it to physically strike enemies. Striking the same enemy a set number of times causes that enemy to be recorded within the Bestiary. The number of hits required varies by monster. When you've satisfied the hit requirement, a sound will play
 

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