In order to unlock the achievement known as Chatterbox, you must speak with the Majin at least one-hundred times.
If you have an arcade fightstick, use it for this achievement.
Make sure you are at a save point. Program the fightstick so that once you hold down the B button, it will be on turbo speed. Face the Majin and just hold down B. You will go in and out of the dialogue very quickly and within a minute or two, the achievement should unlock fairly quickly. Have fun and good luck!