It could be Rain's best friend. This friend might be a very skilled fighter or detective - like character. He would start to search for Rain immediately after learning of the kidnapping. He would follow the clues left behind by Wong Yun Fat and his accomplices. And in a final showdown, he would rescue Rain from Wong Yun Fat's clutches.
Another possibility is that a group of rebels or freedom fighters would save Rain. They might see Rain as a symbol of hope for their cause. When they learn that he has been kidnapped by Wong Yun Fat, they band together. They use their collective strength, knowledge of the land, and some clever strategies to infiltrate Wong Yun Fat's stronghold and rescue Rain.
Perhaps Wong Yun Fat is being controlled by some evil force. This force compels him to kidnap Rain. Rain could be a key figure in some prophecy or something like that. So Wong Yun Fat's actions are not entirely his own will. He takes Rain to a secret location, and Rain has to use his wits to escape while also trying to figure out why Wong Yun Fat is doing this.
Dumbledore would be a likely candidate. He has a long history with Grindelwald and would not let Harry be in danger at Grindelwald's hands.
One possible theme could be rescue. If Rain G is kidnapped by Yun Fat, then the story might revolve around someone coming to rescue Rain G.
Themes in this kind of fanfiction can be quite diverse. There could be a theme of mystery, like why Wong kidnapped Rain in the first place. Is there some hidden agenda or secret that Rain is a part of? Another possible theme is the relationship between the captor and the captive. It could start as a hostile relationship but develop into something more complex over time, such as an unexpected bond or understanding. Additionally, themes of survival and escape might be present as Rain tries to find a way out of the situation.
I'm sorry, I haven't come across such specific 'yun fat kidnaps rain g gundam fanfiction' stories, so I can't recommend any directly.
I'm sorry I can't provide you with a particular 'wong kidnaps rain fanfiction' story. But if it's a relatively niche or new concept, you could try reaching out to relevant fan communities. There are often forums or groups dedicated to specific types of fanfiction. You can post there asking if anyone has written or knows of such a story. Also, be cautious when exploring new fanfiction as some might contain elements that are not in line with your preferences.
Maybe Damon could save her. He's always been protective of those he cares about and he's not afraid to take on Klaus.
Most likely, Mario would be the one to save Luigi. He has a strong bond with his brother and would stop at nothing to rescue him.
It could be Naruto. Naruto has a strong bond with Sakura and would sense that something was wrong. He'd probably track her down using his amazing sense of smell or by asking around. Once he found Sasori, Naruto would use his Rasengan and his newfound Sage Mode powers to take on Sasori and rescue Sakura.
Annabeth would most likely be the first one to try to rescue Percy. She and Percy have a deep connection, and she wouldn't stand by while he's in danger. She's smart and resourceful, so she'd come up with a plan to find out where Aphrodite has taken him and then figure out a way to get him back.