What are some interesting ideas for an 'Attack on Titan' and 'Titanfall' crossover fanfiction?

One idea could be that the Soul Reapers have to enter the world of Attack on Titan to stop Hollows that are being created by the Titans' negative energy. Another could be that Eren Jaeger somehow gains Soul Reaper powers and uses them to fight both Titans and Hollows. Maybe Ichigo could end up in the walls and teach the Survey Corps his sword - fighting techniques to better combat the Titans.

One idea could be that Mel, a character from another universe perhaps, has some unique ability that can help the Survey Corps in 'Attack on Titan' deal with the Titans. For example, if Mel can manipulate time, she could freeze the Titans in place, giving the soldiers a chance to attack without risk. Another idea is that Mel accidentally ends up in the world of 'Attack on Titan' and has to learn the ways of survival there. She could form an unlikely friendship with Eren or Mikasa and together they discover new ways to fight the Titans.

Another interesting concept is that some of the Titans could be modeled after the RWBY characters' weapons or fighting styles. For instance, a Titan with a scythe - like weapon similar to Ruby's Crescent Rose, and it could have a special ability based on her speed and agility.

The characters from 'Attack on Titan' would have a mixed reaction to the 'Titanfall' technology. Some, like Armin, would be very interested in understanding how it all works. He would study the technology and come up with new strategies for using it against the Titans. Others might be more hesitant. Levi, for instance, might be skeptical at first but would eventually see the value. They would need to adapt to things like the energy systems, which are very different from what they are used to. They would also have to learn new combat maneuvers that are designed around the 'Titanfall' technology.

Perhaps the friendly titan is a protector of a certain area outside the walls that the humans have not explored much. The story could be about the Survey Corps making an alliance with this titan. The titan guards the area from other dangerous titans, and in return, the humans help the titan when it gets injured. This could lead to a whole new understanding of the titan world and how they can co - exist with the friendly ones.

One idea could be that the Titans from Titanfall end up in the world of RWBY. They could team up with the Huntsmen and Huntresses to fight a new, powerful Grimm threat that is too much for either side to handle alone. The Pilots could share their advanced combat skills with the RWBY characters, and in return, the RWBY characters could teach the Pilots about the use of Aura and Semblances.

One idea could be the Pilots from Titanfall teaming up with the Normandy crew in Mass Effect. They could share their combat skills and technology. For example, the Pilots' parkour abilities might amaze the Mass Effect characters, and in return, the advanced biotics and tech of the Mass Effect universe could be useful for the Titanfall side.

One idea could be that your OC is a new recruit in the military and gradually gains the attention and affection of various popular characters like Eren, Levi, and Armin. They are all drawn to the OC's unique skills and personality.

A male OC in an Attack on Titan fanfiction could be a double agent. He pretends to be on the side of the Titans while actually working for the Survey Corps. He could have been captured by the Titans as a child and raised among them, but his human instincts and loyalty to his own kind make him turn against the Titans. Another interesting idea is a male OC who is a healer. In a world full of Titan attacks, most of the focus is on combat, but a healer OC could bring a new dimension to the story. He could develop new medical techniques to treat the wounded soldiers, and his struggle to keep people alive in the face of such danger could be a great plot point. And also, a male OC who is a historian, trying to uncover the secrets of the past about the Titans and the origin of the walls.

One idea could be exploring an alternate timeline where the main characters have different Titan powers. For example, Eren could have the Colossal Titan's power from the start. Another could be a story centered around a new character who joins the Survey Corps and has a unique ability to communicate with Titans on a deeper level. Maybe they try to find a peaceful coexistence with the Titans instead of just fighting them all the time.