One possible fanfic plot could be that Eren has been planning this for a long time. He might gather intelligence about the Colossal Titan's weaknesses. Then, in a fierce battle, he manages to get close enough to deliver a fatal blow. This could be a very emotional moment for him as well, considering the history between them.
Well, sometimes he uses his titan's speed and agility to dodge the Colossal Titan's attacks and then strike at its nape. It's a classic way to take down a titan in the Attack on Titan universe.
In DC Comics, Colossal Boy is a notable character. Created by DC, his character has been explored by various artists over the years, including Dave Cockrum in what is mentioned as '1 story'. Colossal Boy's power of growing large gives him an edge in many situations. He can tower over foes, lift heavy objects, and be a force to be reckoned with. Regarding Cockrum's story, it could be that Colossal Boy was part of a team - up, or perhaps he was facing a particular villain that only his powers could defeat. But without delving deeper into that one story, we can only speculate on the exact nature of his appearance and role in it.
Power and responsibility are common themes. Since Izuku has this colossal form, he has to learn to use it wisely. Another theme could be self - discovery as he figures out what he can do with his new power.
One popular colossal science fiction novel is 'Dune' by Frank Herbert. It has a vast and complex universe with unique political, ecological, and religious systems. Another is 'Foundation' by Isaac Asimov, which presents a grand vision of a galactic empire's rise and fall. And 'Hyperion' by Dan Simmons also stands out. It weaves together multiple storylines in a richly detailed future setting.
I'm not familiar with an 'IRG 1' in relation to DC LSH Colossal Boy. It could be something very specific or a less - known part of the lore. Without more information, it's hard to say what the story would be specifically in that context.
Eren could be an interesting choice. Since he has such a complex character arc already, making him the tenth titan could add another layer to his story. He could struggle with the new power and how it changes his view of the world and his mission.
Armin could also be a main character in such a fanfic. He's known for his intelligence. As a permanent titan, he could use his smarts in unique ways. He might try to figure out the secrets of the titan form from the inside and communicate with the other characters in unexpected ways. For example, he could leave clues or messages for his friends using his titan abilities.
Eren could be an interesting main character in a friendly - titan fanfiction. He has a complex relationship with the titans already. Imagine if he discovers a friendly titan that changes his view of all titans. He could try to understand it better and maybe even learn to control other titans through the knowledge he gains from this friendly one.