In the context of the novel, 'my world bloom for you' might imply a deep emotional connection. It could be that the character's inner self, which was perhaps dull or unfulfilled before, starts to thrive and show all its best aspects due to the presence or influence of 'you'. For example, it could be a story of a person who was lonely and then met someone who made their whole world seem like a beautiful garden in full bloom.
Molly Bloom is the central figure in this true story. Without more context, we can assume she is an individual with a story worth telling, perhaps someone who overcame difficulties or had a remarkable life.
Sky might also be a savior. He has a strong connection with Bloom and would be enraged to find out she's been kidnapped. He could use his combat skills and swordsmanship to fight Brick and rescue Bloom. Another possibility is that Tecna, with her technological skills, could track down Bloom's location and help in the rescue operation.
Some of them might be really amused. For example, Baekhyun could burst out laughing, thinking it's a really interesting and unique thing that fans create such fictional stories. He might even ask you some funny questions about the plot.
Jin could be a bit shy about it at first. But then he would probably start joking around, saying things like 'Oh, what crazy things do they write about me this time?' He would take it in a light - hearted way and enjoy the fact that fans are so passionate about them that they create entire fictional worlds centered around BTS.