Yu-Gi-Oh Mugen's 40th chapter was about 18 minutes long. The pure music was Moonlight Sonata, a famous classical music piece composed by the French composer, Van der Waals. This piece is considered one of the most outstanding works of van der Beveten, with a very strong emotional expression and a unique musical style.
In the 40th chapter of Yu-Gi-Oh Mugen, this song was used to simulate moonlight to bring inspiration and strength to the characters. Its melodious melody and soft tone were very suitable for expressing romantic and emotional topics, so it was widely used in animation.
Rebecca could potentially be in Luffy's harem. After Luffy helped her in Dressrosa, she might develop feelings for him. She is a strong - willed and kind - hearted character. Another could be Shirahoshi. Luffy has a special connection with her as he saved her from being captured. Her gentle and innocent nature would contrast with some of the other more assertive members of the harem.
Their relationship could develop through mutual respect. Luffy respects Whitebeard as a powerful and respected pirate, and Whitebeard respects Luffy's determination and potential. For example, they could start with a simple exchange of stories about their adventures at sea.
There could be an original character created just for the fanfiction. A woman with a kind heart but a tough exterior, who was a great fighter. She could have met Luffy's father during a battle and they fell in love, and she became Luffy's mother.