Definitely not. Pacific Rim has no connection to manga. It was conceived and brought to life specifically as a cinematic production with its own distinct storyline and universe.
Fanfic related to 'Pacific Rim' should focus on aspects like the story, characters, and the world - building of the 'Pacific Rim' universe in a proper way. Any form of sexual fanfic is not in line with the positive and respectful exploration of the original work.
One common theme is the battle between colossal forces. You have Godzilla, a huge and powerful creature, and the Jaegers from Pacific Rim, which are also massive and strong. So, there's often a lot of epic fight scenes.
The 'Pacific Rim Story' could potentially revolve around the unique ecosystems found along the Pacific Rim. It could tell of the diverse marine life, from the colorful coral reefs to the large whales that inhabit those waters. It may also include stories of the indigenous peoples who have lived in harmony with this environment for centuries, their traditions and their relationship with the land and sea. Additionally, it could cover modern-day issues like conservation efforts and the impact of climate change on the Pacific Rim.