Often, it's shown through Peter's internal monologues. He might think about how Morgan gets to have a normal family life with Tony while he has to hide his identity and fight crime. For example, he could be seeing Morgan have a simple dinner with Tony and feel a pang of jealousy because he rarely gets such a normal moment with Tony.
His relationship with Morgan herself could also be affected. He might not be as kind to her as he should be. Instead of seeing her as a little girl who just happens to be in a situation where she gets a lot of attention, he could start to resent her, which would make their interactions awkward and uncomfortable.
It can be shown through his actions too. Maybe Merlin is a bit more snappy or short - tempered with Arthur when he's feeling jealous. Like when Arthur asks Merlin to do a task, Merlin might do it with a bit of an attitude instead of his usual eagerness, because he's jealous of something Arthur has or has done.
Well, in these fanfictions, Sasuke's jealousy can be quite intense. It can be seen when he gets angry or distant when another male character is around Sakura. For example, if a male teammate gets too friendly with Sakura, Sasuke may start to give him the cold shoulder. It's a way to show that Sasuke has deep feelings for Sakura and doesn't like the idea of someone else getting close to her.
Garu's jealousy in Pucca fanfiction is often shown through his actions. He may become more withdrawn or brooding when he sees Pucca with another character. For instance, he might sulk in a corner or train more vigorously as a way to distract himself from his jealous feelings.
Sakura's jealousy of Hinata can be portrayed in a more subtle way too. In some fanfictions, she might distance herself from Naruto when she sees Hinata getting closer to him. Instead of showing her jealousy outwardly, she'll withdraw and become more focused on her training or other friendships. But it's clear to the readers that she's jealous because of the way she'll steal glances at Naruto and Hinata when they're together, and the sad look in her eyes when she does so.
Often, his jealousy is manifested in his actions towards James. He might try to outdo James in academic or magical feats, all because he wants to prove that he is better than James, especially in Lily's eyes. And when it comes to Lily, he may be secretly longing for her attention while trying to hide his feelings because he knows she is with James.
Sakura's jealousy in these fanfictions can also be expressed through her words. She could make snide remarks about Hinata's relationship with Sasuke. Saying things like 'I don't see what he sees in you' or something along those lines. It adds a lot of tension to the story.
Jealousy can be shown through actions. For instance, if Sakura is jealous, she might avoid Itachi. She could also be short - tempered when he tries to talk to her. Just like in real life, people who are jealous often act differently towards the person they're jealous about.
Often, his age is adjusted to fit the type of story the author wants to tell. If it's a coming - of - age story, he'll likely be a teen. For instance, a lot of fanfics set in high school make him 16 or 17. This age allows for exploration of his growth, both as Peter Parker and as Spider - Man.
Some fanfictions portray Peter's asthma as a factor that makes his superheroics more heroic. Despite having this condition that can limit his physical abilities at times, he still manages to swing around the city and fight crime. It gives his character a sense of determination and courage that goes beyond just his superpowers.