One possible plot development is that Thalia tries to hide her crush from everyone, including Percy. She's afraid of being rejected or making things awkward in their group. So she keeps her feelings bottled up, but her actions sometimes give her away, like she's always the first to volunteer to help Percy when he's in a tight spot.
Another plot could be that Thalia decides to be more forward about her feelings. She might confess her crush to Percy, which could lead to a whole range of reactions from him. He could be surprised and not know how to respond at first. Or he could feel the same way and then they start a relationship, which would change the dynamics within their group of friends.
One possible scenario could be that Thalia is constantly trying to find excuses to be around Percy. She might volunteer for quests or tasks that she knows Percy will be involved in just so she can spend time with him.
In some fanfictions, Thalia's huge crush on Percy could lead to some really cute and awkward moments. For example, she could be so flustered around him that she stutters when trying to have a normal conversation. And she might get jealous when she sees other girls getting too friendly with Percy. Maybe she starts leaving little gifts for him anonymously, things she knows he likes, like a special type of food or a small trinket she found on one of her adventures.
One possible plot development could be Hanabi trying to get closer to Naruto. She might start by finding excuses to be in the same place as him, like showing up at his favorite training spots. Another could be her trying to impress Naruto with her skills, perhaps by showing off her new jutsu in front of him. And she could also start to compete with Hinata in a friendly way for Naruto's attention.
Well, Thalia might initially be shocked when she discovers what Gabe is like. She could then start to investigate more about Gabe's background and motives. Maybe she finds out that he has some sort of connection to a minor god or goddess who is using him to cause trouble for Percy. This discovery could lead to a whole new adventure where Thalia has to deal with this god or goddess while also trying to protect Percy and his mom from Gabe.
Another plot could involve female Naruto's friends noticing her crush before she's ready to admit it. They might try to play matchmaker, which could lead to some awkward and funny moments. For instance, if her friends think she has a crush on Kakashi, they could set up situations where she has to be alone with him, like 'accidentally' leaving them together during a mission briefing. This would force female Naruto to deal with her feelings in unexpected ways.
One interesting plot development could be that Thalia's protection of Percy leads to her uncovering a new threat against the demigods. Maybe she discovers a hidden group of monsters that are specifically targeting Percy because of his unique powers. This could then lead to an epic battle where Thalia uses her skills as a daughter of Zeus to fend off the monsters and keep Percy safe.
One possible plot development could be Percy having to face various ancient and terrifying monsters on his own in Tartarus. He might have to use his wits and limited resources to survive. For example, he could encounter the monstrous Titans that were imprisoned there long ago.
Perhaps Percy forms an unexpected alliance in Tartarus. There could be other lost souls or even some ancient beings that have been trapped there. Together, they could plan an escape or a way to overthrow the dark forces that rule Tartarus. This alliance could test Percy's beliefs and values as he has to work with some rather shady characters.
Perhaps Percy joins a special unit in the military. In this unit, he discovers some sort of conspiracy or mystery within the military structure. This could lead him on a journey to uncover the truth while still fulfilling his military duties. He might also face some moral dilemmas along the way as he tries to do what's right for the military as a whole.
They could be like siblings. Percy and Thalia might act as the older siblings, protecting and guiding Nico. Percy, with his leadership skills, and Thalia, with her combat abilities, would be great at looking out for the younger Nico. They could also be like cousins, with a close - knit bond but still having their own individual family heritages that sometimes create interesting dynamics.