To get this you have to get through 9 levels for Nina. 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 Nina are
Level 1 Adversary
900 Hearts
Level 26 Suave
Work at Hunting
Level 2 Nuisance
7,200 Hearts
Level 28 Lucky
Level 28 Mysterious
100,000,000 Dollars
Level 3 Frenemy
59,400 Hearts
Level 30 Lucky
New Car
Solider of Fortune (Hunting)
Level 4 Acquaintance
490,050 Hearts
Level 32 Mysterious
2 New Car
Level 5 Friendzoned
4,165,425 Hearts
Assassin (Hunter)
3 New Car
15 Moonlight Stroll
Level 6 Awkward Besties
35,406,113 Hearts
Level 36 Mysterious
4 New Car
15 Beach
Level 7 Crush
300,951,956 Hearts
One Man Army (Hunting)
5 New Car
15 Sightseeing
Level 8 Sweetheart
2,558,091,956 Hearts
Level 41 Mysterious
6 New Car
15 Movie Theater
Level 9 Girlfriend
21,743,778,839 Hearts
Level 47 Lucky
7 New Car
Work at Slaying