The Secret Words are "evol ustakiA"! - S2.E9

After a blizzard buries Aine and Mio's snow stage, the girls get a surprise when Karen and Mirai show up to help. The idols notice some children watching them and ask if they would like to do Aikatsu, which the children agree to. However after Karen and Mirai confront Alicia, the children suddenly change their mind, not wanting to do Aikatsu anymore. So Mirai decides to play a game to cheer everyone up, no one can say Aikatsu until she says so. Instead everyone must say 'evol ustakiA'.

Note: 'evol ustakiA' is taken from the Japanese 'キスイダツカイア', which is 'アイカツダイス' reversed. This is romanized as "Aikatsu daisuki" or simply "Love Aikatsu"