DRAGON BALL XENOVERSE 2

You will eventually unlock a few houses to go to. When you unlock Majin Buu, you will have to feed him to allow him to get enough strength to give birth. You get food as picks up around the city and you can buy water from a vendor. About 34 water should do the trick. They cost 1,000 Zeni each.

Wouldn't hurt to buy a few extra to give his child to make them transform for another achievement.

Once you have unlocked Buu's House, you are able to enter the building and speak to Majiin Buu himself, offer him food until the bar in the top right has been filled, he will then spawn a smaller Majiin, Unlocking this achievement.

To Gather food easily, and for free, walk around the right side of the map and look for areas of water near water falls, they will always spawn water, or apples which can be used to give to Buu for food. To make the item re-spawn simply complete a quest and go back to the same location and pick up more of the same food, Buu doesn't care.

Other locations include the Namek farm for lettuce, Grandpa Gohans house for fish bones, and the town outside the academy for pudding and chocolate, all re-spawn after a quest completion.

the achievement is at 7:14