Another possibility is that Ash returns with some sort of special mission or knowledge from the war. He might be on a quest to use this new - found knowledge to make changes in his homeland. He could face opposition from those who don't believe in his ideas or are afraid of the changes he wants to bring. This could lead to a story full of adventure and self - discovery.
It's possible that Greninja's return is part of a prophecy in the Alola region. The local people might see Greninja as a sign of great change or a hero. So Ash and Greninja have to work together not just to battle but also to fulfill this prophecy, which could involve saving the Alola region's natural balance or something similar.
Well, perhaps Ash returns physically but is emotionally scarred. Serena would be there to comfort him. They could start by just reminiscing about old times. Then, Ash might introduce Serena to some of his war - time comrades who are also Pokémon trainers. This could lead to a whole new set of storylines involving group adventures, Pokémon battles, and the rebuilding of relationships that were strained during the war.
The fanfiction could start with Natsu's grand return. His friends are overjoyed but soon realize he's different. He might be haunted by the memories of the war. Maybe he lost some dear friends during the war and is now more determined to protect the ones he still has. His return could also trigger some rivalries. There could be those who are jealous of the newfound respect he has earned from the war, or those who think he has become too powerful and might be a threat. This would create a lot of drama and new storylines in the fanfiction.
His best friend from before the war could be a main character. This friend might have been waiting for Ash's return and now has to deal with the changed Ash.
Well, perhaps Ash comes back with new skills and a sense of purpose. He might be determined to protect Serena even more than before. In the fanfiction, he could use his war - learned strategies to deal with any threats that come their way. And their relationship could evolve into a deeper, more mature love as they face new challenges together.
Well, one possibility is that Ash has changed a great deal due to the war. Maybe he has new skills or a more hardened personality. He could struggle to fit back into his old life with Serana. For example, he might be haunted by the memories of the war and find it difficult to be as carefree as he once was with her.
Well, it could be about Ash going back to Kalos to compete in some new Pokemon battles. Maybe he wants to challenge new trainers or participate in a special tournament there.
Well, it could be that Ash disappears on a dangerous quest. His friends in the harem are distraught. When he returns, he might have new powers. And then he has to deal with the changed dynamics in the harem, like some might be angry at him for leaving, while others are just overjoyed to have him back.
In the 'Ash Return from War for Serna Fanfiction', it could be that Ash returns not just as a hero on the surface but is actually a bit of an anti - hero. He might have made some morally ambiguous decisions during the war. When he comes back to Serna, his actions and decisions start to divide the community. Some see him as a savior still, while others are wary of his new - found ways and the secrets he might be hiding.
One possibility could be that Ash comes back from war a changed man. He might have seen a lot of hardships and death, which makes him more mature. When he reunites with Serena, their relationship could be a bit strained at first. Maybe he has some PTSD and Serena has to help him through it, and in the process, their bond deepens more than ever.