I'll be there for you
It was love at first sight for Maron. Chiaki was her cute new neighbor, and her first impression of him is that he was good-looking and honest, just her type! She later finds out what a perv he is, but still can't help falling for him.
Little does she know, Chiaki knows the truth about Maron's secret identity, and he wants to make her stop being a kaitou by getting close to her and making her fall in love with him. Its all part of his brilliant plan. But he never counted on the fact that he might actually end up falling for her...
When Fin informs her that Sinbad is working for the devil, Jeanne is more than ready to take him on to save the world. But then one day, Maron sees Chiaki transforming into Kaitou Sinbad and is shocked! So does this mean that Chiaki, her lover, was actually the devil's advocate this whole time?
But that shock soon turns into hurt after coming to the realization that if he was Sinbad, then everything was planned - from befriending Maron to lying about his feelings for her... She confronts Chiaki about it, and is devastated when he admits the truth.
She tried to forget about him and put on a happy face, but no matter how much she hated him for deceiving her, she couldn't stop loving him. He's the first person she's ever opened up to about her parents. Ever since they left her, Maron's been so lonely and sad, and Chiaki filled that empty void in her heart. He cheered her up by writing his silly little notes to Maron, so that when Maron checked her mailbox, she wouldn't be sad.
Chiaki continued to pursue her, and she eventually forgave him, once she realized that Chiaki genuinely cared about her. But other problems soon surfaced, in the form of Noin Claude, Jeanne's past lover from the 15th century. He tried to break the the two apart by having them battle over Zen, and even tried to steal Maron for himself, but they could never give up on each other.
In the end, even after Fin's betrayal and turning Miyako against her, Maron triumphed and was able to defeat the devil, and most importantly, overcome her loneliness. With Chiaki, Maron was able to find the courage to believe in herself, and find true happiness.