One possible aspect of this fanfiction could be exploring the relationships between Adrien, Marinette, and Luka. Maybe it's a story where their personalities merge in some magical or scientific way. For example, their combined traits could lead to a new superhero or a character with a very unique set of skills and emotions.
Adrien might get jealous of Luka in fanfiction because Luka seems to have a more 'mysterious' allure. He's different from Adrien in many ways. Luka is more of an artist type, while Adrien is more of a public figure. If Luka starts getting the attention of the girl Adrien likes, it's natural for Adrien to feel jealous.
He could also start acting out of character. Maybe he becomes more competitive towards Luka. If they are both in a band or something, Adrien might push himself harder to be better than Luka just to get Marinette's attention. He could also be more snappy or short - tempered with Luka, even if he doesn't mean to be.
One common plot could be that Adrien sees Luka getting closer to Marinette. For example, at a music event where Luka is performing and Marinette is clearly impressed. Adrien might start to feel jealous as he has feelings for Marinette himself. He could then start to act out of character, perhaps being a bit more withdrawn or overly competitive when Luka is around.
Well, Adrien could be jealous of Luka in fanfiction for a number of reasons. For one, Luka has a really cool and unique style. He's also very in tune with his emotions. If in the fanfic Luka is making moves on the girl Adrien likes, like Marinette, then of course Adrien would be jealous. Luka's calm and collected nature might also seem more appealing to some characters in the story, which would irk Adrien.
One common scenario is Adrien seeing Marinette and Luka on a date. He might feel a pang of jealousy and then try to interfere in a clumsy way. Another is when Luka gives Marinette a special gift, like a song he wrote for her, and Adrien gets jealous because he wishes he could do something that unique for Marinette.
There could be a lot of internal conflict. Marinette might be used to her shy yet determined self, and Adrien his more reserved but princely nature, and Luka his laid - back attitude. When merged, they'd have to reconcile these differences within the new entity. This could lead to a very character - driven story as they learn to function as one.
With his other friends, Adrien's jealousy can make him seem preoccupied. If they're all hanging out and Luka and Marinette are interacting, Adrien might not be as engaged in the group activities. His friends might start to wonder what's wrong with him and try to cheer him up, but he'll still be focused on his jealousy towards Luka.
In many such fanfictions, Adrien's jealousy can be a driving force for character development. It might lead to him realizing his true feelings for Marinette. For example, he could start to notice how much he cares when he sees Marinette and Luka having a great time together. This jealousy can create interesting scenarios like Adrien trying to be closer to Marinette or even getting a bit possessive in an endearing way.
One common theme is unrequited love. Maybe Adrien has feelings for Marinette, and when he sees Luka getting close to her, he gets jealous. A plot device could be misunderstandings. For example, Adrien might misinterpret an innocent gesture between Luka and Marinette as something more. Another aspect could be the internal struggle Adrien faces. He might be too shy or afraid to admit his feelings, but the jealousy makes him more aware of them.