One possible plot could be that Akainu attacks the Straw Hat's new island, endangering Luffy's friends. Luffy, filled with rage, challenges Akainu. After an intense battle, Luffy discovers a new form of his Gear ability that allows him to withstand Akainu's magma and finally defeat him.
Considering Luffy's character development, he has always been against those who harm his friends and the innocent. Akainu has caused great harm, especially during the Marineford War. If Luffy continues to grow in strength, and if the story progresses in a way that pits them against each other again, there's a chance. But the Marines also have their own ways of protecting their top - ranked officers, so it's a complex situation.
According to what I know about online novels, the age of the fifth personality, the Emperor Slayer streamer, has not been publicly disclosed. He's a rather mysterious person who doesn't leave much information on the internet, so I can't accurately know his age.
One interesting aspect could be the unique character reactions. For example, seeing how different Servants respond to the events of the Holy Grail War in ways that might deviate from the original storyline. It can also be fascinating to see how fanfic writers explore the relationships between characters in new and unexpected ways.
Archer is often quite popular. His complex personality and his various abilities make him a great character to explore in reaction fanfiction. His snarky remarks and his hidden depths can be really interesting to write about in different reaction scenarios.
I think Shanks would have an interesting reaction. He has known Luffy since he was a kid. Seeing Luffy reach Gear 5, he would probably be proud but also a bit cautious. He might think about how far Luffy has come and also wonder what challenges this new power will bring for Luffy and the world at large.
One common theme is the clash of ideologies. Akainu has a very strict and uncompromising view of justice in his original story, while Naruto has a more forgiving and rehabilitative view. So when they interact in fanfiction, this clash often forms a central theme.
The Qing Emperor called Wu Zhu Old Fifth because they were sworn brothers. Wu Zhu was ranked fifth, so he was called Old Fifth by the Qing Emperor. Ye Qingmei had always followed the principle of equality. When she was alive, she had pulled the Qing Emperor, Chen Pingping, Fan Jian, King Jing, and Wu Zhu to become sworn brothers. Wu Zhu was the youngest and ranked fifth, so the Qing Emperor affectionately called him Fifth. This title also expressed the Qing Emperor's closeness to Wu Zhu and the deep friendship between them.
The Qing Emperor called Wu Zhu Old Fifth because they were sworn brothers. Wu Zhu was ranked fifth, so he was called Old Fifth by the Qing Emperor. Ye Qingmei had always followed the principle of equality. When she was alive, she had pulled the Qing Emperor, Chen Pingping, Fan Jian, King Jing, and Wu Zhu to become sworn brothers. Wu Zhu was the youngest and ranked fifth, so the Qing Emperor affectionately called him Fifth.