how does rudeus get his arm back

No, he doesn't. Tyrese keeps his arm intact throughout the comics.

In certain fanfictions, a magical or spiritual artifact plays a crucial role in Ichigo getting his powers back. This artifact might be something that has a deep connection to his past or his family heritage. It could bestow upon him the energy or the knowledge needed to regain his powers. Maybe it was hidden away for a long time, waiting for the right moment to be discovered by Ichigo.

In the fanfic, it could be that Harry has a very smart friend who helps him come up with a clever plan. For example, they might find a loophole in a contract that the person who has Harry's money was using to keep it. So, by exploiting this loophole, Harry is able to legally get his money back. Another possibility is that Harry has some special skills or powers in the story that he uses to his advantage. He could use his charm to persuade the person who owes him money or his intelligence to outwit them in a negotiation.

In some storylines, Wolverine gets his Adamantium back through complex scientific or magical means. But it varies depending on the specific comic arc.

In some comic storylines, Wolverine gets his adamantium back through complex and unexpected circumstances involving advanced technology or powerful allies.

In some comic storylines, Wolverine regains his adamantium through advanced scientific means or as part of a complex plot twist.

Wolverine's claws can come back due to a combination of factors like his mutant abilities reaching a new peak or a scientific experiment gone right. Different comics offer different explanations for this.

Thor typically gets his hammer back by demonstrating his noble character and commitment to justice. Sometimes, it involves facing difficult trials and showing that he has learned from his past mistakes.

In some storylines, it could be through a special serum or some kind of advanced tech.

Maybe he starts to train with one - armed techniques. He could learn from other one - armed ninjas if there are any in the fanfiction world. His friends would also play a big role. They might encourage him to keep going or help him in his training.