disclaimer: i do not own one piece
Detective Au
Luffy runs a detective agency in Goa city under the name of Strawhat investigations. One day a tall blond woman with blue eyes and a pointy nose came to his office, the woman present herself as Sarie Nantokanette and she came to Luffy's office with a case for him: about a week ago her father and her brother died in a accident and she fears that she could be the next because now she is the only heir to the Nantokanette fortune, she is getting marry in three weeks because her fiancé agreed to postpone the wedding for a month until the mystery could be solved so she wants Luffy to resolve her case and bring the culprit to justice and she is willing to pay him a luxurious amount of money for his service. Luffy accepts her case with three conditions: 1) he and the rest of his agency will move to her house and live there to have better view of the case until the case is closed, 2) Sarie will have in her persona a gun all the time in case the culprit doesn't surrender to justice peacefully and 3) half of the money for the case will be paid in advance and the other half after the case is closed.
Sarie accepts all of the conditions and with that Luffy kiss her hand as a sign that the case is open. the next morning Luffy and his team move to Sarie's house and they were receive formally by the servants and joyfully by Sarie, they were also receive in a cordial manner by Sarie's fiancé: a man called Sterry that looked disgusted to have some commoners in the house but he will have to endure it until the case is closed (Luffy knows Sterry very well from what his brother Sabo told about him so he would be an option for a culprit).
For the next two weeks the Strawhats using their abilities they are trying to solve the mystery and during that time Luffy and Sarie get close one to each other (a fact that Sterry didn't like), before getting the case solve Luffy decide to call Koby a friend of his in the police department to help in this case and to tell Sarie to wait for three days to the case to be resolved. when the three days have passed Luffy tells Sarie that he knows the identity of the culprit but that he will he need her help, in the afternoon Luffy calls Sterry to the office of Sarie's father in which the two of them start talking and at some Sterry reveals by accident that killed Sarie's father and brother: he hear about the Nantokanette fortune when he was a child and decide that he will do anything to get his hands on it, so he start wooing Sarie in order to get access to the fortune but she was the second to be born so he will have to speed up things so he asked for her hand in marriage on the ending of the last month which was the same night that he killed her father and brother and he have agreed that for a whole month the wedding would be postpone until the end of the month.
After his confession Sterry puts out a gun in order to keep his secret hidden forever, that gun was grabbed by Luffy who smashed it until it breaks and after that the Strawhats, Koby and Sarie appear in the office by one of the secret doors in the house. before the police could arrest Sterry Sarie steps in and give her former fiancé a slap in his face and after that the police proceed to arrest Sterry which made Luffy closed the case, two days later he is sentenced to death penalty.
when the Strawhats were packing up their things Luffy tells them that he will stay for another day and that he will see them in the office which they agreed, that night Luffy enters Sarie's room only to see her crying in her desk which mades Luffy tries to comfort her but she tells him to leave because she doesn't want to see him because she believes that nobody loves her and that the only reason why are near her is because of her money. in that moment Luffy steps in and while grabbing her by the shoulder he gives her a passionate kiss on the lips, after they break the kiss Luffy wiped her tears he tells her of how amazing and beautiful she is and how much he does love her; all of this caused in her a blush and tears of joy because someone really loves for who she is and not for what she has. While Sarie was still blushing and crying of joy she asked Luffy to show her much he loves and with that she gives luffy an even more passionate kiss.
-lemon scene-
after the lemon scene Luffy assures that he will always be there for her if she needs him and after that they share one final kiss.