Yo-kai Watch

The Yo-kai Watch is titular item of the Yo-kai Watch franchise, which allows the protaganist Nathan "Nate" Adams / Katie Forester to contact, befriend, summon, and battle yo-kai. In the actual canon, including the canon of the anime, the owner of the watch is "Nate". However if the player picks to alternatively play as Katie in Yo-kai Watch 1 and 2, then she instead is the one who obtained he watch, swapping roles with Nate. Yo-kai who are befriended give the owner their medal, which can be inserted into the watch to summon the yo-kai to the protaganist's aide. Wearing the watch allows them to see yo-kai, who are invisible to other humans, and they can use the watch's lens to reveal a yo-kai that is hiding itself.

The official creator of the watch is the yo-kai Steve Jaws (parody of Steve Jobs ), however the actual creator was the protaganist's grandfather (either Nathaniel Adams in the main canon, or Kenny Forester, if you play as Katie), who created the first model of the watch. Steve Jaws then created a mass-produced version, which is sold in the yo-kai world that yo-kai can buy. It's implied that due to this, there are actually plenty of other humans who were given a watch by a yo-kai, and are in a similiar situation to Nate. Indeed, there are plenty of examples of evidence of such a thing in the games, which show multiple instances of others who can interact with yo-kai.

Types
The ordinary Yo-kai Watch used by Nate is a wrist watch, which allows him to insert and summon yo-kai with normal medals. This is the ordinary type that was mass-produced and sold by Yopple Inc, and was given to Nate when he freed Whisper from the Crank-a-kai machine.



Katie's watch
The watch that is given to Katie has the same funtions as the ordinary watch, although instead of being a wrist watch, it's a pink pocket watch that she wears around her neck.



Yo-kai Watch Model Zero
The original yo-kai watch which was created by Nathaniel Adams / Kenny Forester 60 years ago. It can detect "wicked yo-kai", something that the normal modern watch can't do due to the feature not being needed any more. It can summon yo-kai who have Z-medals, as well as yo-kai with classic medals, and wicked yo-kai too. Normal yo-kai medals cannot be used in it though.