This is a pun based off Fukukitaru's name and a Japanese proverb, as listed on her Wiki page. The proverb is "Warau kado ni wa fuku kitaru" (笑う門には福来たる), and means that good things come to happy people. As a fun fact, the original owner of the real life Matikanefukukitaru also owned a horse named Matikanewaraukado.