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.
In this fanfiction, the two central characters are Ace and Luffy. Ace, being the older brother, is likely to be the more protective and guiding one. Luffy, on the other hand, is full of energy and curiosity, always ready for an adventure. Their different personalities will surely lead to many interesting events in the story.
In this kind of fanfiction, Ace might take Luffy on an adventure to find a hidden treasure. They could encounter various powerful enemies and strange islands along the way.
Luffy would probably be super excited. He's always been on this big adventure, and meeting his dad would be like a new milestone. He might jump up and down and start asking a million questions right away, like what his dad has been doing all this time and if he has any cool stories from his own adventures.
If he asks Hinata, she would probably be overjoyed. She has always been in love with Naruto, so her answer would most likely be an immediate 'yes' with tears of happiness in her eyes.
Well, Chopper in a really comical and out - of - the - box fanfic could transform into a human girl (through some wacky magic or something) and give Luffy a kiss just for fun. Usopp's sister (if we assume he has one in the fanfic) who has heard all about Luffy's adventures and is a big admirer could be the one kissing him. And then there's always the chance that it could be a random girl from an island they visit. Maybe she's a baker's daughter and Luffy saved her bakery from being burned down by pirates, so she gives him a kiss as a thank you.
He could be secretly touched. Deep down, Snape has a complex personality. Even though he doesn't show it easily, the fact that Hermione, a bright and determined student, gives him a gift might reach his softer side and make him feel a bit of warmth.
Sakura might be initially shocked and worried. She'd be concerned about how this new entity within Naruto could affect his health and stability. But she'd also be curious to see if this could give them an edge in future battles.
Hermione would be furious. She's a strong - minded and independent witch. She would probably immediately start looking for ways to escape or fight back. She might try to use her knowledge of magic to find a loophole in whatever situation Draco has created to force her into marriage.