Each character in Octopath Traveler has their own unique Talent that they can make use of. And one character, H’aanit the Hunter, has the unique ability to capture and then summon monsters that you encounter in the game world.
To capture these creatures all you have to do is scroll down to the Beast Lore option in the action menu when playing as H’aanit in combat, and then select the Capture option. But of course it isn’t that simple.
Just like in any Pokemon game, you need to wear down the health of these monsters and inflict status effects on them to have a better chance of capturing them. Do so, and the percentage of success that appears when attempting to capture them increases.
Get the percentage up to a high enough number and you can easily capture them without much of a hassle.
Once captured, these monsters can then be summoned in combat with the Summon Beast skill. Keep in mind though that their strength and skills as a summon can be seen beforehand on the very same menu where you get the option to initiate the capture.