He could be getting married to Ochaco Uraraka. They have a great friendship and there are many hints in the series that suggest a deeper connection between them. Their personalities complement each other well, with Deku's determination and Ochaco's cheerfulness.
One possible fanfiction could be that Deku discovers his new Black Whip quirk during a particularly intense battle. He's facing off against a powerful villain and in a moment of extreme stress, the quirk just emerges. It starts as a small tendril and then grows rapidly, helping him to bind the villain and turn the tide of the fight.
Deku's One For All power could be seen as a sort of super - strong magic in the Fairy Tail universe. It could be that he has to learn to control it in a different way, like using the Fairy Tail guild's training methods. Maybe he'd have to combine it with some form of Fairy Tail magic to make it even more powerful.
One common plotline could be Deku trying to hide his sickness from his friends at U.A. High so as not to worry them. He might keep pushing himself during training, which could lead to him collapsing eventually. Another could be his friends finding out about his illness and rallying around him to help him get better, like bringing him home - made soup and study notes so he doesn't fall behind in class.
Another storyline might involve Deku having to face some sort of villain threat right before the wedding. He has to balance protecting his loved ones and ensuring the wedding goes on as planned. Maybe a new villain emerges who wants to disrupt the harmony of the event. But with the help of his friends and his own heroic skills, Deku manages to defeat the villain and still have a wonderful wedding.
Bakugou could use his words. He might tell Deku that he believes in him. For example, he could say 'Deku, you may be a nerd but you're a strong nerd.' It's a backhanded compliment but it shows he has faith in Deku.
Well, Deku does lose his quirk. However, this event leads to new developments and challenges for him. It's a crucial plot twist that adds depth to the story.
One possible source could be some kind of ancient and forbidden jutsu. Maybe there was a long - lost scroll in the Hidden Leaf Village that when Naruto accidentally opened it, the power of the Hollows somehow transferred into him. Another source could be an encounter with a mysterious being from another dimension. This being, seeing Naruto's potential, decided to bestow him with hollow powers for some unknown reason.