Buy Luck Incense and give it to Chansey. Bring Chansey and a Ditto to a Day Care. Have Chansey hold the Luck Incense. Eventually, Chansey will lay an egg that will hatch into a Happiny.

How do you get the Happiny egg sword?

Bring the Chansey and a Ditto to Day Care and let Chansey hold the Luck Incense. After some time, Chansey will lay an egg that will give you a Happiny. All you need to do now is to ride around and move around the area until the egg hatches and you have your Happiny.

Where do you find Happiny in Pokemon Ultra Sun?

In Pokémon Sun and Moon and Pokémon Ultra Sun and Ultra Moon, Happiny can be caught in the wild at Route 1, Route 4, Route 5, Route 6, Hau'oli City and Lush Jungle when called on by a Pichu, Igglybuff or Bonsly in an S.O.S. Battle.