I've got another girl to power up to Level 80 that I'm currently trying to reach. Which My next girl is Hitomi.
Interesting note: Level 80 is how you get 11th Character Episode (which is the last episode to get) for certain character, which all the girls have 11 cutscenes each. Cutscenes level up your Owner EXP which extends your play time.
The secret to level up is:
1. Have your main girls to completing events & grind until you complete missions mainly for trendy tickets (depending in certain events Free V-Stones)
2. If you wind up getting a costume that isn't your main, put 1 of your main in Lesson (or put all 2 main if you manage to get 2 trendy outfits that aren't your main)