To get this you have to get through 9 levels for Mio. Each level has up to 4 goals you must complete to reach the next level. The possible goals are, reaching a specific number of hearts, reaching a specific amount of money, giving specific gifts, taking the girls on dates, reaching a specific level in your hobbies/jobs.
The goals for Mio are
Level 1 Adversary
200 Hearts
Level 3 Suave
Level 2 Nuisance
560 Hearts
Level 4 Motivation
1337 Dollars
Level 3 Frenemy
1,708 Hearts
Level 5 Funny
Rose
Onion Dehydrator (Fast food)
Level 4 Acquaintance
5,209 Hearts
Level 7 Tenderness
Hand Lotion
Barista (Restaurant)
Level 5 Friendzoned
17,191 Hearts
2 Moonlight Strolls
Donut
Level 9 Funny
Level 6 Awkward Besties
56,730 Hearts
2 Beach
Book
Work at Zoo
Level 7 Crush
187,210 Hearts
Sightseeing
Drink
Level 12 Smart
Level 8 Sweetheart
617,794 Hearts
Flowers
Movie Theater
Level 14 TechSavvy
Level 9 Girlfriend
2,038,719 Hearts
Cake
Engineer (Computers)
Level 18 Funny