Fiona Meets Big Hero 6

Fiona Is a Princess In Mewni, But Before Her 14th Birthday She Escapes Due to Being Jealous of Her Former Best Friend Star Butterfly, She Then Meets Hiro And His Family Then Moves In With Them, After Hiro And Fiona Graduated High School Early They Begin Doing Bot-Fights Together As Friends, After Fiona's 14th Birthday She And Hiro Became Best Friends.......................................................................................................................... With Benefits, After Tadashi's Death Fiona Was Thinking of Returning To Mewni So That Hiro Can Be Safe From Danger, But Hiro Wanted Her To Stay, Mewman Or Not He Still Wants Her To Stay On Earth, They Then Started To Track Down Tadashi's Murderer, Then They Formed The Superhero Team (One-Time Only) Called "Big Hero 7"

Fiona's Adventure Series Season 1, Episode 1 - Fiona Comes To Earth

Timeline: During "Star Comes To Earth"