Expect The Unexpected

A new student enters the playing field, shy and quiet but kind and generous. While everyone else is excited, greeting Rosemary happily and with open arms(even Chloe), Lila however, sees Rosemary as another threat against her chances with Adrien. When Lila catches her talking with Adrien and Marinette, she quickly grows jealous. Angry at the possibility of Rosie seeing through her lies, she threatens to turn everyone against her if she doesn't leave Adrien alone. Rosie is soon caught up in her fears as Lila's falsehoods about her reach everyone, degrading her budding romance with Nathaniel. Mari catches Rosie crying a few days later and wants to help, telling her after school that she wants to talk to her the next day. However, when Mari shows up at their meeting spot and finds little trace of her, she begins to suspect the worst, unaware that help will come from an unexpected source. Meanwhile, Mari's feelings for Chat Noir grow and she is soon faced with a difficult decision. Will she ignore her feelings for her partner and keep going after Adrien or accept them and forget about her first love?
Disclaimer: This is a self-insert for Miraculous Ladybug but there are changes to the canon storyline, such as aging up the characters. As for the ages, since they're a little inconsistent, I'm gonna have them all start at the ages of 14-15 and have 5 yrs pass so it's easier to know their ages.
Marinette, Alya, Chloe, Mylene, Alix, Rose, Sabrina, Lila, Kagami, Mireille, Aurore and Zoe: 19 yrs. old
Rosie(the self-inserted character): 19 yrs.
Nino, Adrien, Ivan, Kim, Max, Nathaniel, Marc: 19 1/2yrs. old
Luka & Juleka: 20 yrs. old
NOTE: I WAS writing this as S4 was coming out, so be warned that aspects of my storyline are different than the canon one. I'm mostly following the canon storyline but bc of plot stuff in S4, it's hard to stay on target and keep the major canon storylines, so I will only be staying canon(plot-wise)up to E4, Sentibubbler, Rocketear, & Wishmaker.