best way to reach 99?

so I wanna reach level 99 and beat simon and I'm currently using sciel maelle and verso and all 3 of them are 60-65 and I want to level them up without using those xp farms I want to play the game and do challenges. what things can I do (in order) and not smth too hard that needs lvl 70s or 80s. do many things and can reach 99 while collecting good weapons and pictos on the journey (idk if spoiler so I marked it just incase)