In this fanfiction, there could be a powerful enemy from Natsu's past who resurfaces. This enemy targets Princess Hisui to get back at Natsu. Natsu, of course, won't let that happen. He stands in the enemy's way and a fierce battle ensues. Since the enemy knows Natsu's weaknesses well, they manage to wound him. But Natsu's determination to protect Hisui gives him the strength to keep fighting until help arrives.
One possible plot could be that there is an attack on the kingdom where Princess Hisui resides. Natsu, being the brave character he is, jumps into action. As he battles the invaders, he gets hurt while making sure no harm comes to the princess. Maybe the invaders have some sort of dark magic that Natsu underestimates, and it catches him off - guard, resulting in his injury.
Well, perhaps there's a traitor within the princess's court. This traitor sets a trap for the princess. Natsu senses the danger and tries to stop it. In the process of protecting Hisui from the various threats within the trap, like poisoned darts or collapsing structures, he sustains injuries. The story could then focus on how Natsu recovers and also on finding out the identity of the traitor.
One common theme is sacrifice. Natsu is willing to put himself in harm's way for the princess, which shows his selfless nature. Another theme could be loyalty, as he is loyal to the princess and to the idea of protecting the innocent. Also, there might be a theme of recovery, as Natsu has to recover from his injuries, which can show his strength and the support he gets from his friends and the princess herself.
One possible plot could be that Shinra and Maki are in a dangerous situation, like in a battle against a powerful foe. Shinra steps in front of Maki to shield her from an attack, getting hurt in the process. Maki then has to find a way to either heal Shinra or get them both to safety while still fending off the enemy. It could also involve some emotional moments where Maki realizes how much Shinra is willing to sacrifice for her.
One possible fanfiction plot could be during a village invasion. Naruto, with his unwavering sense of justice and his growing feelings for Hinata, shields her from an enemy's attack. He might get seriously injured, which then spurs Hinata to tap into her own hidden power to defend him in return. This kind of story can explore their bond deeper and show how they support each other in tough times.
One possible scenario could be that Shinra and Iris are in a battle against some powerful demons. Shinra tries his best to shield Iris from the demons' attacks. As he does so, he gets seriously injured but still manages to hold off the demons long enough for backup to arrive. Iris is deeply moved by his selfless act and vows to become stronger to protect him in the future.
There could be a fanfiction where Naruto and Ino are exploring an ancient ruin. Unbeknownst to them, there are traps everywhere. When a huge boulder starts rolling towards Ino, Naruto pushes her out of the way. He gets crushed under the boulder's edge. Ino is desperate to save him. She manages to find some herbs in the ruin that have healing properties and uses her medical knowledge to treat Naruto's injuries. Meanwhile, Naruto's willpower also helps him in his recovery.
In many Beast Boy and Raven fanfictions, Beast Boy's act of protecting Raven is quite common. When he gets hurt in the process, it often adds a layer of drama. Maybe he takes a blow meant for Raven during a battle with a powerful villain. This could lead to Raven realizing her deeper feelings for him as she tends to his wounds.
It could be that Natsu underestimates the strength of the final boss guarding Princess Hisui. During the intense battle, he takes several hard hits but refuses to give up. He endures the pain and uses his last bit of strength to defeat the enemy and save the princess.
In the fanfiction, Natsu and Hisui's relationship could develop through shared goals. For example, they might both be on a quest to save their land from a common enemy. During this journey, they rely on each other's strengths. Natsu's physical power and Hisui's intelligence and diplomatic skills could complement each other. As they face challenges together, they start to see each other in a new light. This mutual respect and admiration could turn into love, and finally result in their marriage.
In a plotline, the enemy might be after Vivi for some political reason. Luffy steps in without hesitation. He gets hurt but his determination to protect Vivi doesn't waver. This could lead to the Straw Hat crew coming together in a new way to face the threat. For example, Nami could use her navigation skills to find a safe haven where Luffy can recover while the others hold off the enemy.
Maybe they are in a forest filled with dangerous magical creatures. A giant snake - like creature lunges at Annabeth. Percy quickly moves in front of her and the creature bites his leg. In another situation, they are in a magical maze. There are walls closing in on them and spikes starting to protrude from the sides. Percy pushes Annabeth out of the way of a spike that was about to impale her, but he gets scratched all over his body. And they could be in a fight against a powerful sorcerer. The sorcerer casts a spell of dark energy towards Annabeth, and Percy uses his own power to try and block it. However, some of the dark energy seeps through and causes internal damage to Percy.