Obviously, cloud would be the main character. There could also be his boss, who is constantly frustrated by cloud's actions. Maybe there's a coworker who tries to help cloud, thinking he's just having a bad time, not realizing he actually wants to get fired.
One possible plot could be that cloud is tired of his current job situation. Maybe he has a difficult boss or uninteresting tasks. So, he starts to intentionally make mistakes at work, like coming in late, not meeting deadlines, or being rude to clients in an attempt to get fired.
There are several possible motives. Cloud could be seeking revenge on his employer for some wrong done to him. By getting fired in a spectacular way, he could be aiming to damage the company's reputation. Another reason might be that he has a new opportunity lined up that he can't take while still employed. Or maybe he's just a bit of a rebel and getting fired is part of his non - conformist attitude.
I'm not familiar with this particular fanfic. But usually, when a character tries to get fired, there could be underlying issues in the story's world. It could be related to conflicts with superiors, a sense of being trapped in a role that doesn't suit the character, or a plot device to lead the character into a new and different situation. Without reading the fanfic, this is all just speculation.
Well, he might start by constantly being late to work. Maybe he shows up hours after his shift is supposed to begin, wearing inappropriate clothing for the Shinra environment. He could also be very insubordinate to his superiors, like openly defying orders from Rufus or Heidegger.
Cloud might try to physically attack one of the important Shinra executives. Let's say he punches Rufus right in the face during a meeting. That would be a very extreme measure and would surely lead to him getting fired immediately. Another extreme thing he could do is set off false alarms in the Shinra building all the time, causing chaos and disrupting the normal operations of the company.
Mr. Krabs would surely be a main character. After all, he's the one who fires Squidward. He might be portrayed as the bad guy in the story, or perhaps there could be some backstory that makes his decision seem more understandable.
Well, one possible plot could be that Squidward gets fired because he finally snaps at Mr. Krabs over his cheapskate ways. He then has to figure out how to pay his bills and find a new job. Maybe he tries to start his own art business but struggles with marketing it.
It could be a new administrator at the school who has a very different vision of how hero training should be conducted. This person might see Aizawa's methods as too old - fashioned or too lax, even though they are actually effective. So, they push for his dismissal.
Obviously, Percy would be one of the main characters. And probably some of his classmates who are with him on the ship that gets wrecked.
I don't know as I haven't read the fanfiction. It could be a young adventurer who is intrigued by the cloud and sets out to explore it. Maybe there's a wise old character who gives advice about the cloud's significance.