In many fanfics, Naruto gets stronger through unique training regimens. For example, he might encounter a powerful mentor who teaches him new jutsu or ways to enhance his chakra control. This could involve intense physical and mental exercises that push his limits far beyond what he learned in the original series.
In fanfiction, Ichigo might get stronger through unique training regimens. For example, he could be trained by a long - lost powerful Shinigami. This Shinigami might have ancient techniques that are not known to the regular Soul Society. Ichigo would have to endure rigorous physical and spiritual training, pushing his limits far beyond what he thought possible.
In fanfiction, Master Chief can get stronger through various means. One way is by facing tougher and more diverse enemies. Each encounter forces him to adapt and improve his combat skills, making him stronger over time. Another way could be by getting access to new and advanced technology. For example, if he gets a more powerful weapon or enhanced armor, it can significantly boost his capabilities in combat.